feat: NewOpenAPIService OASVersion dispatch + parameter format support

[erraggy]

Context

This PR is a follow-up to PR#125 which introduced the oastools builder integration. It addresses feedback from the maintainer regarding NewOpenAPIService behavior and adds parameter format support that achieves feature parity with the legacy BuildSwagger path.

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Summary

NewOpenAPIService Enhancement

• NewOpenAPIService now dispatches based on Config.OASVersion:
  • OAS 3.x versions → uses BuildOAS3
  • OAS 2.0 → uses BuildOAS2
  • Unset/default → falls back to legacy BuildSwagger

Parameter Format Support

• Add support for param.DataFormat() using oastools v1.33.0 WithParamFormat
• Previously, formats like "uuid", "date", "date-time", and "int64" were ignored
• Now properly propagated to the OpenAPI spec for both OAS 2.0 and 3.x output

Code Quality Improvements

• BuildOAS2/BuildOAS3 now call Config.Validate() to catch configuration errors early
• Extract shared response option building into buildResponseOptions helper
• Add formatBinary constant to satisfy goconst linter

Changes

• Upgrade oastools dependency to v1.33.0
• Implement WithParamFormat in mapParameter() function
• Add comprehensive tests for parameter format in both OAS 2.0 and OAS 3.x output
• Improve error handling with early config validation

Test plan

• All existing tests pass
• New tests verify parameter format for uuid, date, date-time, int64
• Tests for NewOpenAPIService OAS version dispatching
• Linter passes with no issues
• Coverage: 72.9%

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