refactor: built in openapi generator

[akfaiz]

Description

• Refactor this library to use built-in openapi generator with reflection mechanism
• Support openapi 3.2
• Close echoopenapi adaptor breaks with path parameters when request option is missing #38

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactor / code quality
• Other (describe):

Checklist

• make check passes locally (sync + tidy + lint + test)
• Tests added or updated to cover the change
• Golden files updated if spec output changed (make test-update)
• Relevant documentation updated (README, adapter README, etc.)
• Commit messages follow Conventional Commits

Notes for Reviewers

[llamapreview]

AI Code Review by LlamaPReview

🎯 TL;DR & Recommendation

Recommendation: Request Changes

This PR modernizes the OpenAPI generator to use a built-in model and reflection, but introduces a compilation error in an internal mapper file due to a renamed type (openapi.OAuthFlowsImplicit → openapi.OAuthFlow), and leaves CONNECT method support inconsistently gated across adapters.

📄 Documentation Diagram

This diagram documents the new OpenAPI generation flow using the built-in generator with reflection.

sequenceDiagram
    participant Client
    participant Router as spec.Router
    participant Gen as Generator
    participant Reflector as Reflector
    participant Doc as openapi.Document
    Client->>Router: NewRouter(opts...)
    Router->>Gen: create generator
    Client->>Router: Post(path, opts...)
    Router->>Gen: Register route
    Client->>Router: Get(path, opts...)
    Router->>Gen: Register route
    Client->>Router: MarshalYAML()
    Router->>Gen: buildOnce()
    Gen->>Reflector: reflect schemas from Go types
    Reflector-->>Gen: *openapi.Schema
    Gen->>Doc: build OpenAPI document
    note over Router,Doc: PR replaces external swaggest library<br/>with owned OpenAPI model and reflector
    Router-->>Client: YAML/JSON output

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🌟 Strengths

• Solid golden-file test updates ensuring deterministic output changes are reviewed.

Priority	File	Category	Impact Summary	Anchors
P1	adapter/chiopenapi/router_test.go	Bug	Stale OAuthFlowsImplicit type blocks compilation	path:internal/mapper/openapi3.go
P2	adapter/chiopenapi/router.go	Architecture	CONNECT gating not applied to other adapters
P2	Makefile	Testing	Fragile coverage aggregation, less readable output
P2	adapter/chiopenapi/router_test.go	Testing	Raw byte diff makes tests fragile to formatting

🔍 Notable Themes

• Inconsistent CONNECT version gating: Only Chi adapter checks openapi.Version320 before skipping CONNECT; other adapters silently ignore it with OpenAPI 3.2.
• Test fragility: Replacing semantic YAML comparison with byte comparison will cause false-positive failures on formatting changes.

📈 Risk Diagram

This diagram illustrates the stale mapper reference risk introduced by the type rename.

sequenceDiagram
    participant Test as Test (router_test.go)
    participant Mapper as internal/mapper/openapi3.go
    participant OpenAPIPkg as openapi package
    Test->>OpenAPIPkg: uses openapi.OAuthFlow (new type)
    OpenAPIPkg-->>Test: compiles fine
    Mapper->>OpenAPIPkg: references openapi.OAuthFlowsImplicit (old type)
    OpenAPIPkg-->>Mapper: type not found – compile error
    note over Mapper: R1(P1): Stale reference to removed type<br/>breaks build of internal/mapper

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[codecov]

Codecov Report

❌ Patch coverage is 83.52436% with 115 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/reflect/tags.go	79.67%	21 Missing and 17 partials ⚠️
internal/reflect/reflector.go	84.72%	14 Missing and 8 partials ⚠️
internal/builder/utils.go	79.54%	9 Missing and 9 partials ⚠️
internal/reflect/converter.go	81.52%	10 Missing and 7 partials ⚠️
internal/builder/builder.go	89.42%	6 Missing and 5 partials ⚠️
internal/builder/operation.go	85.18%	4 Missing and 4 partials ⚠️
adapter/ginopenapi/router.go	0.00%	0 Missing and 1 partial ⚠️

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