[OCaml][Fix] Unreferenced enum + Direct recursive types (#23005)

* [OCaml] Fix bugs around enum parsing

Problem: The OCaml client generator threw IllegalArgumentException: Unreferenced enum when encountering enums inside composed schemas
  (anyOf/allOf/oneOf).

Root Causes:
1. The enum collection logic didn't traverse into composed schemas
2. The enum hashing used order-dependent string concatenation, causing lookups to fail when enum values appeared in different orders
3. Enums directly within composed schema branches (not in properties) weren't collected

Solution:

1. Added composed schema support:
  - New `collectEnumSchemasFromComposed()` method handles `anyOf/allOf/oneOf`
  - New `collectEnumSchemasFromList()` method recursively processes composed schema branches
  - Enums directly in composed schemas (not just in properties) are now collected
2. Refactored enum hashing to use Set:
  - Changed from comma-joined strings to `TreeSet<String>` for order-independent, collision-free hashing
  - Handles edge cases like empty string enums `""`
3. Added test case:
  - Tests enums in nested composed schemas
  - Tests enum with empty string value in anyOf

* OCaml: Add support for direct recursive types

* OCaml: Fix enums in anyOf

* OCaml: fix recursive types

* Fix recursion tests

* Fix recursive types, improve tests

* [OCaml] Improve title of generated README.md

.github/workflows/samples-ocaml.yaml

@@ -7,12 +7,16 @@ on:
       - 'samples/client/petstore/ocaml-fake-petstore/**'
       - 'samples/client/petstore/ocaml-oneOf-primitive/**'
       - 'samples/client/petstore/ocaml-additional-properties/**'
+      - 'samples/client/petstore/ocaml-enum-in-composed-schema/**'
+      - 'samples/client/petstore/ocaml-recursion-test/**'
   pull_request:
     paths:
       - 'samples/client/petstore/ocaml/**'
       - 'samples/client/petstore/ocaml-fake-petstore/**'
       - 'samples/client/petstore/ocaml-oneOf-primitive/**'
       - 'samples/client/petstore/ocaml-additional-properties/**'
+      - 'samples/client/petstore/ocaml-enum-in-composed-schema/**'
+      - 'samples/client/petstore/ocaml-recursion-test/**'
 
 jobs:
   build:
@@ -26,12 +30,14 @@ jobs:
           - 'samples/client/petstore/ocaml-fake-petstore/'
           - 'samples/client/petstore/ocaml-oneOf-primitive/'
           - 'samples/client/petstore/ocaml-additional-properties/'
+          - 'samples/client/petstore/ocaml-enum-in-composed-schema/'
+          - 'samples/client/petstore/ocaml-recursion-test/'
     steps:
       - uses: actions/checkout@v5
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3
         with:
-          ocaml-compiler: 5
+          ocaml-compiler: 5.3
       - name: Install
         run: opam install . --deps-only --with-test
         working-directory: ${{ matrix.sample }}