Add support for path aliases (oapi-codegen#2312)

* Add support for path aliases
Closes oapi-codegen#223

When an OpenAPI spec uses $ref to alias one path to another (e.g.
/test2: $ref: '#/paths/~1test'), kin-openapi inlines the referenced
path item into both entries. Previously this produced duplicate
ServerInterface methods, wrapper functions, and type definitions —
generating Go code that never compiled.

Detect internal path aliases via PathItem.Ref (only when it starts
with "#/paths/", to distinguish from external file references). For
alias operations:

- Server: skip interface method, wrapper, and strict handler generation.
  Route registration still emits both paths, pointing to the canonical
  wrapper via the new HandlerName() method on OperationDefinition.

- Client: generate methods with a suffixed OperationId (e.g.
  GetTestAlias0) so each aliased path gets its own request builder
  targeting the correct URL.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: skip operationId write-back for alias operations

Alias paths share the same *openapi3.Operation pointer as the canonical
path. Writing the suffixed alias name (e.g. GetTestAlias0) back to
op.OperationID would corrupt the canonical operation's ID in the
embedded spec.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mromaszewicz

internal/test/pathalias/client-config.yaml

@@ -0,0 +1,5 @@
+# yaml-language-server: $schema=../../../../configuration-schema.json
+package: pathalias
+generate:
+  client: true
+output: client.gen.go

internal/test/pathalias/client.gen.go

@@ -0,0 +1,4 @@
+package pathalias
+
+//go:generate go run github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen --config=server-config.yaml spec.yaml
+//go:generate go run github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen --config=client-config.yaml spec.yaml

internal/test/pathalias/doc.go

@@ -0,0 +1,6 @@
+# yaml-language-server: $schema=../../../../configuration-schema.json
+package: pathalias
+generate:
+  chi-server: true
+  models: true
+output: server.gen.go