Improve error handling and serialization features

[Syati]

Description of the changes

This pull request introduces the following enhancements and refactorings:

• Enhanced error handling with structured options for to_hash, as_json, and messages methods.
• Added documentation covering advanced usage, error handling, serialization, and integration with strong parameters.
• Refactored to_hash method to use symbols for keys in nested error structures and configured it to support structured options.
• Added custom key transformation and error handling for nested attributes using StructuredParams.
• Refactored error handling logic to comply with RuboCop standards and introduced optional boolean parameter validations.
• Developed a new error formatting module that supports JSON Pointer references.

Why these changes are introduced

The changes improve the robustness and flexibility of error handling, particularly for complex nested structures. They also ensure better integration with advanced features like strong parameters and enhance user support with improved documentation.

Additional notes

• These changes ensure compliance with coding standards and enhance readability.
• No breaking changes have been introduced.

[Copilot]

Pull Request Overview

This PR introduces enhanced error handling and serialization features for StructuredParams, including a new custom Errors class with structured error formatting capabilities, improved documentation, and refactored internal methods to better support nested structures.

• Enhanced error handling with structured/flat format options for to_hash, as_json, and messages methods
• Added comprehensive documentation covering installation, usage, validation, serialization, and integration patterns
• Refactored parameter validation logic to use symbols consistently and improved error path formatting

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
spec/errors_spec.rb	New comprehensive test suite for the custom Errors class
sig/structured_params/params.rbs	Updated type signatures for refactored parameter validation methods
sig/structured_params/errors.rbs	New type definitions for the custom Errors class
sig/structured_params.rbs	New type definitions for the main module
lib/structured_params/params.rb	Refactored validation methods and error handling logic
lib/structured_params/errors.rb	New custom Errors class with structured formatting support
lib/structured_params.rb	Added errors module import and updated type registration
docs/*	New comprehensive documentation files
README.md	Streamlined README with links to detailed documentation
README_ja.md	Updated Japanese README with same improvements

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