- Add File parameter class in openapi/params.py with binary format schema
- Implement comprehensive multipart/form-data parsing in openapi_validation.py
  * Support for WebKit and standard boundary formats
  * Base64-encoded request handling for AWS Lambda
  * Mixed file and form data parsing
- Update dependant.py to handle File parameters in body field resolution
- Add comprehensive test suite (13 tests) covering:
  * Basic file upload parsing and validation
  * WebKit boundary format support
  * Base64-encoded multipart data
  * Multiple file uploads
  * File size constraints validation
  * Optional file parameters
  * Error handling for invalid boundaries and missing files
- Add file_parameter_example.py demonstrating various File parameter use cases
- Clean up unnecessary imports and pragma comments

Resolves file upload functionality with full OpenAPI schema generation and validation support.

- Break down _parse_multipart_data method into smaller helper methods
- Reduce cognitive complexity from 43 to under 15 per SonarCloud requirement
- Improve code readability and maintainability
- All existing tests continue to pass

Helper methods created:
- _decode_request_body: Handle base64 decoding
- _extract_boundary_bytes: Extract multipart boundary
- _parse_multipart_sections: Parse sections into data dict
- _parse_multipart_section: Handle individual section parsing
- _split_section_headers_and_content: Split headers/content
- _decode_form_field_content: Decode form field as string

Addresses SonarCloud cognitive complexity violation while maintaining
all existing functionality for File parameter multipart parsing.

…to feature/file-parameter-clean

…test

- Created dedicated _convert_uploadfile_to_bytes() function for type conversion
- Removed conversion logic from _normalize_field_value() to preserve its original intent
- Updated both call sites to chain normalize → convert → validate
- Added explanatory comment for __all__ in params.py to document public API intent

Addresses reviewer feedback about separation of concerns between normalization
(structural changes) and conversion (type transformations/IO operations).

The test was calling _normalize_field_value expecting UploadFile→bytes conversion,
but we moved that logic to _convert_uploadfile_to_bytes as part of the separation
of concerns refactoring.

The openapi directory needs an __init__.py to be recognized as a Python package
by the documentation build system (mkdocstrings). Added a descriptive docstring
to document the module's purpose without exporting any symbols.