Enum case matching by remaining buffer length

[FlickerSoul]

This PR adds support of matching enum case using remaining buffer length. This matching method is exclusive with byte matching.

The changes (implementation, test, and specs) are reviewed by the owner.

[Copilot]

Pull request overview

This PR adds support for matching enum cases using remaining buffer length via a new @match(length:) macro. This enables binary format parsing where variants are determined by data length rather than discriminator byte patterns.

Key Changes:

• Added @match(length:) macro for non-consuming length-based matching
• Enforced mutual exclusivity between byte-based and length-based matching strategies
• Implemented __matchLength(length:in:) utility function for buffer length checking

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
openspec/changes/add-match-length/proposal.md	Documents the rationale and impact of adding length-based enum matching
openspec/changes/add-match-length/specs/parse-enum/spec.md	Specifies requirements for length-based matching and mutual exclusivity validation
openspec/changes/add-match-length/tasks.md	Task breakdown for implementing the feature
Tests/BinaryParseKitTests/TestEnumParsing.swift	End-to-end tests covering length matching with various scenarios including default fallback
Tests/BinaryParseKitMacroTests/BinaryParseKitEnumTests.swift	Macro expansion tests for length matching and mixed strategy diagnostics
Sources/BinaryParseKit/BinaryParseKit.swift	Public macro declaration with comprehensive documentation and usage examples
Sources/BinaryParseKit/Utils/ParsingUtils.swift	Utility function implementation for non-consuming length checks
Sources/BinaryParseKitMacros/Macros/Supports/Constants.swift	Added constant for matchLength utility function
Sources/BinaryParseKitMacros/Macros/ParseEnum/ParseEnumMacroError.swift	Added error message for mixed matching strategies
Sources/BinaryParseKitMacros/Macros/ParseEnum/ParseEnumCase.swift	Validation logic to enforce matching strategy mutual exclusivity
Sources/BinaryParseKitMacros/Macros/ParseEnum/EnumCaseParseInfo.swift	Data structures supporting both byte and length matching targets
Sources/BinaryParseKitMacros/Macros/ParseEnum/ConsructParseEnumMacro.swift	Code generation for length-based matching conditions and printer intel

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