fix(parsing): drop TextFormatT parameterization in parse_response (#3084)

Closes #3084.

parse_response() called construct_type_unchecked with three types
parameterized by a free TypeVar (ParsedResponseOutputText[TextFormatT],
ParsedResponseOutputMessage[TextFormatT], ParsedResponse[TextFormatT]).

Pydantic cannot resolve a free TypeVar, so model_rebuild(raise_errors=False)
returns False on every invocation. MockCoreSchema._built_memo only caches
the rebuilt schema when model_rebuild succeeds; when it fails, the cache
is never set and a new Rust-backed SchemaValidator/SchemaSerializer is
allocated on every parse_response() call.

Result: heavy pydantic-core objects leak without bound whenever
AsyncResponses.parse() is called in a long-lived process. This is
observable as a flame-graph spike (see #3084 for the screenshot).

Fix (per issue author's diagnosis): drop the [TextFormatT]
parameterization at the runtime type_= argument. At runtime Python's
generics are erased anyway — the constructed object's type is
identical either way. Only the pydantic schema rebuild path differs:
with the non-parameterized generic, model_rebuild succeeds and the
schema is cached in _built_memo.

Tests: all 5 existing tests in tests/lib/responses/test_responses.py
continue to pass (verified locally). No behavior change for callers.

Signed-off-by: Mukunda Katta <mukunda.vjcs6@gmail.com>

Author: MukundaKatta

src/openai/lib/_parsing/_responses.py

@@ -68,7 +68,11 @@ def parse_response(
 
                 content_list.append(
                     construct_type_unchecked(
-                        type_=ParsedResponseOutputText[TextFormatT],
+                        # Drop the TextFormatT parameterization: pydantic cannot resolve a free
+                        # TypeVar so model_rebuild() always returns False, which means
+                        # MockCoreSchema._built_memo is never populated and a new Rust-backed
+                        # SchemaValidator is allocated on every call. See issue #3084.
+                        type_=ParsedResponseOutputText,
                         value={
                             **item.to_dict(),
                             "parsed": parse_text(item.text, text_format=text_format),
@@ -78,7 +82,8 @@ def parse_response(
 
             output_list.append(
                 construct_type_unchecked(
-                    type_=ParsedResponseOutputMessage[TextFormatT],
+                    # See note above: non-parameterized generic keeps the schema cache hot.
+                    type_=ParsedResponseOutputMessage,
                     value={
                         **output.to_dict(),
                         "content": content_list,
@@ -130,7 +135,10 @@ def parse_response(
             output_list.append(output)
 
     return construct_type_unchecked(
-        type_=ParsedResponse[TextFormatT],
+        # See note above: non-parameterized generic keeps the schema cache hot.
+        # At runtime Python's generics are erased, so the constructed object's type
+        # is identical either way — only the pydantic schema rebuild path differs.
+        type_=ParsedResponse,
         value={
             **response.to_dict(),
             "output": output_list,