Add except option to assert_request_schema_confirm to allow
intentionally omitting required parameters when testing error responses
(401, 400, etc.) while still validating other parameters.

Features

• Exclude specific parameters from validation by type (headers, query, path, body)
• Support multiple parameters in each type simultaneously
• Validate that non-excepted parameters still raise errors when missing

Implementation

• Add ExceptParameter class with handler pattern for each param type
• Refactor QueryHandler, PathHandler, BodyHandler using BaseHashParameterHandler
  to eliminate code duplication (DRY principle)
• Use rack.request.query_hash for query parameters with ||= initialization
• Use prefixed keys (e.g., query:page, path:id) in original_values hash to:
  • Distinguish parameters with same names in different locations
  • Identify correct storage location during restoration
• Store original values before applying dummy values and restore them after validation to:
  • Prevent test environment pollution (dummy values leaking between tests)
  • Maintain test independence and avoid flaky tests
  • Ensure restoration even when validation raises errors (using ensure block)

Tests

• Add comprehensive test cases for all parameter types
• Add /test_except_validation endpoint for testing except behavior
• Verify non-excepted parameters still raise validation errors

Documentation

• Add usage examples with generic parameter names to README.md
• Document except option for error response testing scenarios
• Add YARD documentation following committee gem conventions