fix(parser): fix ColumnEnd for string and f-string literals

StringLiteral used Previous.Value.Length for ColumnEnd, but Value
excludes quotes. Use Previous.Length (which returns SourceLength
when available) to include the full source extent with quotes.

FStringLiteral set ColumnEnd to the FStringEnd token's column
without accounting for the token's length. Add endToken.Length
so ColumnEnd is one past the closing quote, consistent with other
node types.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antonsynd

src/Sharpy.Compiler/Parser/Parser.Primaries.cs

@@ -101,7 +101,7 @@ private Expression ParsePrimary()
                         LineStart = startLine,
                         ColumnStart = startColumn,
                         LineEnd = Previous.Line,
-                        ColumnEnd = Previous.Column + Previous.Value.Length,
+                        ColumnEnd = Previous.Column + Previous.Length,
                         Span = GetSpanFromToken(token)
                     };
                 }
@@ -118,7 +118,7 @@ private Expression ParsePrimary()
                         LineStart = startLine,
                         ColumnStart = startColumn,
                         LineEnd = Previous.Line,
-                        ColumnEnd = Previous.Column + Previous.Value.Length,
+                        ColumnEnd = Previous.Column + Previous.Length,
                         Span = GetSpanFromToken(token)
                     };
                 }

src/Sharpy.Compiler/Parser/Parser.Types.cs

@@ -660,7 +660,7 @@ private FStringLiteral ParseSegmentedFString(int startLine, int startColumn, Tok
             LineStart = startLine,
             ColumnStart = startColumn,
             LineEnd = endLine,
-            ColumnEnd = endColumn,
+            ColumnEnd = endColumn + endToken.Length,
             Span = GetSpanFromTokens(startToken, endToken)
         };
     }