Add comprehensive CI/CD infrastructure

GitHub Actions workflows:
- ci.yml: Multi-platform builds (Linux/macOS/Windows), sanitizers, minimal deps
- code-quality.yml: Formatting, static analysis, security scanning, coverage
- release.yml: Automated releases with cross-platform assets

Code quality tools:
- .clang-format: Google-based C++20 formatting rules
- .clang-tidy: Comprehensive static analysis configuration

Testing infrastructure:
- doctest integration for unit tests
- Mock implementations for testing interfaces
- CMake test discovery and CTest integration

Build system improvements:
- Updated CMakeLists.txt for llmcpp with proper dependencies
- Example projects structure
- Stub implementations for all components to enable CI builds

All components are stubs/placeholders - ready for CI/CD validation

Author: lucaromagnoli

.clang-format

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+---
+BasedOnStyle: Google
+Language: Cpp
+Standard: c++20
+
+# Indentation
+IndentWidth: 4
+TabWidth: 4
+UseTab: Never
+ContinuationIndentWidth: 4
+IndentCaseLabels: true
+IndentPPDirectives: BeforeHash
+
+# Line length
+ColumnLimit: 100
+ReflowComments: true
+
+# Braces
+BreakBeforeBraces: Attach
+BraceWrapping:
+  AfterClass: false
+  AfterControlStatement: false
+  AfterEnum: false
+  AfterFunction: false
+  AfterNamespace: false
+  AfterStruct: false
+  AfterUnion: false
+  BeforeCatch: false
+  BeforeElse: false
+
+# Spacing
+SpaceBeforeParens: ControlStatements
+SpaceInEmptyParentheses: false
+SpacesInParentheses: false
+SpacesInSquareBrackets: false
+SpaceAfterCStyleCast: false
+SpaceBeforeAssignmentOperators: true
+SpaceBeforeCpp11BracedList: false
+SpaceBeforeCtorInitializerColon: true
+SpaceBeforeInheritanceColon: true
+SpaceBeforeRangeBasedForLoopColon: true
+
+# Alignment
+AlignAfterOpenBracket: Align
+AlignConsecutiveAssignments: false
+AlignConsecutiveDeclarations: false
+AlignEscapedNewlines: Left
+AlignOperands: true
+AlignTrailingComments: true
+
+# Breaking
+AllowAllArgumentsOnNextLine: true
+AllowAllConstructorInitializersOnNextLine: true
+AllowAllParametersOfDeclarationOnNextLine: true
+AllowShortBlocksOnASingleLine: Never
+AllowShortCaseLabelsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: Empty
+AllowShortIfStatementsOnASingleLine: Never
+AllowShortLoopsOnASingleLine: false
+AllowShortLambdasOnASingleLine: All
+
+# Breaking before binary operators
+BreakBeforeBinaryOperators: None
+BreakBeforeTernaryOperators: true
+BreakConstructorInitializers: BeforeColon
+BreakInheritanceList: BeforeColon
+BreakStringLiterals: true
+
+# Constructor initializers
+ConstructorInitializerAllOnOneLineOrOnePerLine: true
+ConstructorInitializerIndentWidth: 4
+
+# Includes
+IncludeBlocks: Preserve
+SortIncludes: true
+SortUsingDeclarations: true
+
+# Penalties (for line breaking decisions)
+PenaltyBreakAssignment: 2
+PenaltyBreakBeforeFirstCallParameter: 19
+PenaltyBreakComment: 300
+PenaltyBreakFirstLessLess: 120
+PenaltyBreakString: 1000
+PenaltyBreakTemplateDeclaration: 10
+PenaltyExcessCharacter: 1000000
+PenaltyReturnTypeOnItsOwnLine: 200
+
+# Pointer and reference alignment
+DerivePointerAlignment: false
+PointerAlignment: Left
+
+# Namespaces
+NamespaceIndentation: None
+CompactNamespaces: false
+
+# Access modifiers
+AccessModifierOffset: -4
+
+# Comments
+ReflowComments: true
+CommentPragmas: '^ IWYU pragma:'
+
+# Macros
+MacroBlockBegin: ''
+MacroBlockEnd: ''
+
+# Experimental
+ExperimentalAutoDetectBinPacking: false
+BinPackArguments: false
+BinPackParameters: false
+
+# C++11/14/17/20 specific
+Cpp11BracedListStyle: true
+FixNamespaceComments: true 

.clang-tidy

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+---
+# clang-tidy configuration for llmcpp
+Checks: >
+  -*,
+  bugprone-*,
+  cert-*,
+  clang-analyzer-*,
+  concurrency-*,
+  cppcoreguidelines-*,
+  google-*,
+  hicpp-*,
+  misc-*,
+  modernize-*,
+  performance-*,
+  portability-*,
+  readability-*,
+  -bugprone-easily-swappable-parameters,
+  -cert-err58-cpp,
+  -cppcoreguidelines-avoid-magic-numbers,
+  -cppcoreguidelines-pro-bounds-pointer-arithmetic,
+  -cppcoreguidelines-pro-type-vararg,
+  -google-runtime-references,
+  -hicpp-avoid-magic-numbers,
+  -hicpp-vararg,
+  -misc-non-private-member-variables-in-classes,
+  -modernize-use-trailing-return-type,
+  -readability-magic-numbers,
+  -readability-named-parameter
+
+WarningsAsErrors: ''
+HeaderFilterRegex: '.*'
+FormatStyle: file
+InheritParentConfig: false
+
+CheckOptions:
+  # Naming conventions
+  - key: readability-identifier-naming.ClassCase
+    value: CamelCase
+  - key: readability-identifier-naming.ClassMemberCase
+    value: camelCase
+  - key: readability-identifier-naming.ClassMemberSuffix
+    value: '_'
+  - key: readability-identifier-naming.ConstantCase
+    value: UPPER_CASE
+  - key: readability-identifier-naming.EnumCase
+    value: CamelCase
+  - key: readability-identifier-naming.EnumConstantCase
+    value: CamelCase
+  - key: readability-identifier-naming.FunctionCase
+    value: camelCase
+  - key: readability-identifier-naming.GlobalConstantCase
+    value: UPPER_CASE
+  - key: readability-identifier-naming.LocalConstantCase
+    value: camelCase
+  - key: readability-identifier-naming.LocalVariableCase
+    value: camelCase
+  - key: readability-identifier-naming.MemberCase
+    value: camelCase
+  - key: readability-identifier-naming.NamespaceCase
+    value: lower_case
+  - key: readability-identifier-naming.ParameterCase
+    value: camelCase
+  - key: readability-identifier-naming.PrivateMemberSuffix
+    value: '_'
+  - key: readability-identifier-naming.ProtectedMemberSuffix
+    value: '_'
+  - key: readability-identifier-naming.PublicMemberCase
+    value: camelCase
+  - key: readability-identifier-naming.StaticConstantCase
+    value: UPPER_CASE
+  - key: readability-identifier-naming.StaticVariableCase
+    value: camelCase
+  - key: readability-identifier-naming.StructCase
+    value: CamelCase
+  - key: readability-identifier-naming.TemplateParameterCase
+    value: CamelCase
+  - key: readability-identifier-naming.TypeAliasCase
+    value: CamelCase
+  - key: readability-identifier-naming.TypedefCase
+    value: CamelCase
+  - key: readability-identifier-naming.UnionCase
+    value: CamelCase
+  - key: readability-identifier-naming.VariableCase
+    value: camelCase
+
+  # Function length
+  - key: readability-function-size.LineThreshold
+    value: 100
+  - key: readability-function-size.StatementThreshold
+    value: 50
+  - key: readability-function-size.BranchThreshold
+    value: 15
+  - key: readability-function-size.ParameterThreshold
+    value: 8
+
+  # Complexity
+  - key: readability-function-cognitive-complexity.Threshold
+    value: 15
+
+  # Performance
+  - key: performance-for-range-copy.WarnOnAllAutoCopies
+    value: true
+  - key: performance-move-const-arg.CheckTriviallyCopyableMove
+    value: true
+  - key: performance-type-promotion-in-math-fn.IncludeStyle
+    value: google
+
+  # Modernize
+  - key: modernize-loop-convert.MaxCopySize
+    value: 16
+  - key: modernize-loop-convert.MinConfidence
+    value: reasonable
+  - key: modernize-pass-by-value.IncludeStyle
+    value: google
+
+  # Misc
+  - key: misc-throw-by-value-catch-by-reference.CheckThrowTemporaries
+    value: true
+
+  # Google style
+  - key: google-readability-braces-around-statements.ShortStatementLines
+    value: 1
+  - key: google-readability-function-size.StatementThreshold
+    value: 50
+  - key: google-readability-namespace-comments.ShortNamespaceLines
+    value: 1
+  - key: google-readability-namespace-comments.SpacesBeforeComments
+    value: 2