docs: update for new API

[ianlewis]

Description:

Update documentation to reflect the new CustomLexer and Parser APIs.

Related Issues:

Fixes #173

Checklist:

• Review the CONTRIBUTING.md documentation.
• Add a reference to a related issue in the repository.
• Add a description of the changes proposed in the pull request.
• Add unit tests if applicable.
• Update documentation if applicable.
• Add a note in the CHANGELOG.md if applicable.

[Copilot]

Pull request overview

This PR updates the documentation to reflect changes in the CustomLexer and Parser APIs, specifically the removal of the context.Context parameter from state interface methods in favor of passing context through dedicated context objects (CustomLexerContext and ParserContext).

Changes:

• Updated interface method signatures to remove context.Context parameters from LexState.Run() and ParseState.Run()
• Revised documentation to clarify that context objects are passed to state methods
• Reorganized documentation sections, moving lexer invocation examples before CustomLexer details

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
parser.go	Removed ctx parameter name from ParseState.Run() interface method
lexparse.go	Updated function comment to mention concurrent token feeding
custom.go	Removed ctx parameter name from LexState.Run() interface method
README.md	Updated all documentation and code examples to reflect new API signatures and context object usage

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