docs/imporve documentaions

[lcweden]

This pull request introduces several improvements focused on documentation, API clarity, and internal code quality. The main highlights are the addition of a detailed performance guide, expanded and clarified option types with documentation comments, and minor internal consistency improvements. These changes enhance usability, maintainability, and discoverability for users and contributors.

Documentation improvements:

• Added a comprehensive docs/performance.md file with real-world memory benchmarks, code samples, and explanations for various high-throughput streaming scenarios using the library.
• Expanded the package.json keywords to improve discoverability and updated the description for clarity.

API documentation and type improvements:

• Added detailed JSDoc comments to all option types for decoder/encoder and streaming APIs (JSONTextDecoderOptions, JSONTextEncoderOptions, JSONTextDecoderStreamOptions, JSONTextEncoderStreamOptions, JSONTextLineStreamOptions, JSONTextSelectorStreamOptions). This clarifies usage and available options for each API. [1] [2] [3] [4] [5] [6]
• Added documentation for the Kind type in src/types/kind.ts to describe all possible JSON token kinds.
• Added documentation and improved structure for base, decoder, and encoder options in src/types/options.ts, making option inheritance and available flags clearer.

Internal consistency and bug fixes:

• Fixed access to private fields in Token and Value classes (this.bytes → this.#bytes, this.kind → this.#kind) to ensure encapsulation and correctness. [1] [2] [3] [4]
• Clarified canonicalization terminology in Value to reference RFC 8785 explicitly.