feat(openapi-generator): Improved OpenAPI schema generation

[youngjungithub]

This update enhances the OpenAPI specification generation with several improvements:

1. Numeric type handling:

• Changed number to integer type for integer schemas
• Added proper numeric constraints (minimum/maximum/multipleOf) for:
  • Regular numbers
  • BigInt values (now properly formatted as int64)
  • String-encoded numbers

2. Special type handling:

• Added proper format for UUID strings
• Improved date/time formatting
• Added JSON string format support
• Better handling of numeric unions

3. Parameter processing:

• Removed redundant explode and style parameters
• Added parent/paramName context for better schema inference
• Improved handling of numeric constraints in unions

4. Fix minimum/maximum bug in openapi.ts and add tests for numeric constraints

• Fixed a bug in openapi.ts where minimum and maximum values were swapped
• Added comprehensive tests for numeric constraints in openapi.ts
• Ensured all custom mappings in openapi.ts are properly tested
• Fixed the handling of undefined minimum and maximum values

[youngjungithub]

Todo:

1. Ensure all new functionality (lines of code may act as a proxy) is under test. This will prevent accidental regression in the future.
2. Add any test cases necessary to ensure every custom mapping is under test.