Add TOON format encoding and decoding functionality (#2)

* Add TOON format encoding and decoding functionality

- Implement StringUtils for string manipulation, including escaping and unescaping.
- Create ValidationShared for key validation and safety checks.
- Introduce ToonDecodeOptions and ToonEncodeOptions for customizable encoding/decoding settings.
- Develop ToonDecoder for parsing TOON format strings into JsonNode objects.
- Implement ToonEncoder for converting data structures into TOON format strings.
- Add ToonFormatException for error handling during parsing and encoding.
- Create unit tests for ToonDecoder and ToonEncoder to ensure functionality and data integrity.
- Remove outdated UnitTest1.cs file.

* Update src/ToonFormat/Constants.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/ToonFormat/Internal/Encode/Normalize.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/ToonFormat/Internal/Encode/Encoders.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Optimize parsing performance and fix potential issues
Optimize the performance of the `ParseDelimitedValues` and `ToParsedLines` methods:
- Reduce memory allocation by using `StringBuilder` and `ReadOnlySpan<char>`.
- Allocate capacity in advance to avoid dynamic resizing.
- Replace string operations with more efficient logic.
Fix the code formatting and logic of `IsArrayHeaderAfterHyphen` and `ParseStringLiteral`:
- Adjust the format of the `return` statement.
- Eliminate redundant code.
New `MapRowValuesToPrimitives` method:
- Supports mapping string arrays to JSON primitive values.
Other minor optimizations:
- Fixed the logic for handling blank lines.
- Replaced some string operations with more efficient implementations.
- Fixed the issue of character encoding in comments, improving code readability.

* Update src/ToonFormat/Internal/Encode/Encoders.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/ToonFormat/Internal/Encode/Normalize.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Unified logic for negative zero normalization of floating-point numbers, and a new FloatUtils utility class has been added.
Introduce the FloatUtils utility class and provide the NormalizeSignedZero method,
to uniformly handle the logic of negated zero normalization for floating-point numbers, replacing the original repetitive implementations.
Update the relevant code in Parser.cs and Normalize.cs to enhance readability.
Add the NearlyEqual method for approximate comparison of floating-point numbers.
Delete the references to the Internal\Shared\ folder.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 239573049

src/ToonFormat/Class1.cs

@@ -0,0 +1,92 @@
+using System;
+
+namespace ToonFormat
+{
+
+    public static class Constants
+    {
+        public const char LIST_ITEM_MARKER = '-';
+
+        public const string LIST_ITEM_PREFIX  = "- ";
+
+        // #region Structural characters
+        public const char COMMA = ',';
+        public const char COLON = ':';
+        public const char SPACE = ' ';
+        public const char PIPE = '|';
+        public const char HASH = '#';
+        // #endregion
+
+        // #region Brackets and braces
+        public const char OPEN_BRACKET = '[';
+        public const char CLOSE_BRACKET = ']';
+        public const char OPEN_BRACE = '{';
+        public const char CLOSE_BRACE = '}';
+        // #endregion
+
+        // #region Literals
+        public const string NULL_LITERAL = "null";
+        public const string TRUE_LITERAL = "true";
+        public const string FALSE_LITERAL = "false";
+        // #endregion
+
+        // #region Escape/control characters
+        public const char BACKSLASH = '\\';
+        public const char DOUBLE_QUOTE = '"';
+        public const char NEWLINE = '\n';
+        public const char CARRIAGE_RETURN = '\r';
+        public const char TAB = '\t';
+
+        // #region Delimiter defaults and mapping
+        public const ToonDelimiter DEFAULT_DELIMITER_ENUM = ToonDelimiter.COMMA;
+
+        /// <summary>Default delimiter character (comma).</summary>
+        public const char DEFAULT_DELIMITER_CHAR = COMMA;
+
+        /// <summary>Maps delimiter enum values to their specific characters.</summary>
+        public static char ToDelimiterChar(ToonDelimiter delimiter) => delimiter switch
+        {
+            ToonDelimiter.COMMA => COMMA,
+            ToonDelimiter.TAB => TAB,
+            ToonDelimiter.PIPE => PIPE,
+            _ => COMMA
+        };
+
+        /// <summary>Maps delimiter characters to enum; unknown characters fall back to comma.</summary>
+        public static ToonDelimiter FromDelimiterChar(char delimiter) => delimiter switch
+        {
+            COMMA => ToonDelimiter.COMMA,
+            TAB => ToonDelimiter.TAB,
+            PIPE => ToonDelimiter.PIPE,
+            _ => ToonDelimiter.COMMA
+        };
+
+        /// <summary>Returns whether the character is a supported delimiter.</summary>
+        public static bool IsDelimiterChar(char c) => c == COMMA || c == TAB || c == PIPE;
+
+        /// <summary>Returns whether the character is a whitespace character (space or tab).</summary>
+        public static bool IsWhitespace(char c) => c == SPACE || c == TAB;
+
+        /// <summary>Returns whether the character is a structural character.</summary>
+        public static bool IsStructural(char c)
+            => c == COLON || c == OPEN_BRACKET || c == CLOSE_BRACKET || c == OPEN_BRACE || c == CLOSE_BRACE;
+        // #endregion
+    }
+
+    /// <summary>
+    /// TOON's unified options configuration, styled to align with System.Text.Json. Used to control indentation,
+    /// delimiters, strict mode, length markers, and underlying JSON behavior.
+    /// </summary>
+    public enum ToonDelimiter
+    {
+        /// <summary>Comma ,</summary>
+        COMMA,
+
+        /// <summary>Tab \t</summary>
+        TAB,
+
+        /// <summary>Pipe |</summary>
+        PIPE
+    }
+
+}

src/ToonFormat/Constants.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace ToonFormat.Internal.Converters
+{
+    /// <summary>
+    /// Normalizes double NaN/Infinity to null when writing JSON, keeping original numeric precision otherwise.
+    /// Reading still uses default handling, no special conversion.
+    /// Purpose: Consistent with TS spec (NaN/±Infinity -> null), and provides stable JsonElement for subsequent TOON encoding phase.
+    /// </summary>
+    internal sealed class DoubleNamedFloatToNullConverter : JsonConverter<double>
+    {
+        public override double Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            => reader.GetDouble();
+
+        public override void Write(Utf8JsonWriter writer, double value, JsonSerializerOptions options)
+        {
+            if (double.IsNaN(value) || double.IsInfinity(value))
+            {
+                writer.WriteNullValue();
+                return;
+            }
+            writer.WriteNumberValue(value);
+        }
+    }
+}

src/ToonFormat/Internal/Converters/DoubleNamedFloatToNullConverter.cs

@@ -0,0 +1,24 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace ToonFormat.Internal.Converters
+{
+    /// <summary>
+    /// Normalizes float NaN/Infinity to null when writing JSON; reading keeps default behavior.
+    /// </summary>
+    internal sealed class SingleNamedFloatToNullConverter : JsonConverter<float>
+    {
+        public override float Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            => reader.GetSingle();
+
+        public override void Write(Utf8JsonWriter writer, float value, JsonSerializerOptions options)
+        {
+            if (float.IsNaN(value) || float.IsInfinity(value))
+            {
+                writer.WriteNullValue();
+                return;
+            }
+            writer.WriteNumberValue(value);
+        }
+    }
+}