test(api): move fine-tuning positional tests out of generated code (#3706)

- [x] I understand that this repository is auto-generated and my pull
request may not be merged

## Changes being requested

Keep the fine-tuning positional-argument regression coverage in
handwritten
tests, then restore the two generated test files to the recorded public
generated snapshot. The generated examples use `fine_tuning_job_id=` and
their
original fake `after` values; the original positional calls remain
tested.

Only three test files change. Runtime code, dependencies, the API
reference,
compiler inputs, and generation metadata are unchanged.

## Additional context & links

All 20 original methods and their client parameterizations are retained
verbatim in

[`tests/lib/test_fine_tuning_positional_arguments.py`](https://github.com/openai/openai-python/blob/4dd138db112ee8d02c6803e0f0b812c5c9be3dee/tests/lib/test_fine_tuning_positional_arguments.py):

-
[`TestCheckpoints`](https://github.com/openai/openai-python/blob/4dd138db112ee8d02c6803e0f0b812c5c9be3dee/tests/lib/test_fine_tuning_positional_arguments.py#L14)
and
[`TestAsyncCheckpoints`](https://github.com/openai/openai-python/blob/4dd138db112ee8d02c6803e0f0b812c5c9be3dee/tests/lib/test_fine_tuning_positional_arguments.py#L65)
  preserve `test_method_list`, `test_method_list_with_all_params`,
  `test_raw_response_list`, `test_streaming_response_list`, and
  `test_path_params_list`.
-
[`TestJobs`](https://github.com/openai/openai-python/blob/4dd138db112ee8d02c6803e0f0b812c5c9be3dee/tests/lib/test_fine_tuning_positional_arguments.py#L118)
and
[`TestAsyncJobs`](https://github.com/openai/openai-python/blob/4dd138db112ee8d02c6803e0f0b812c5c9be3dee/tests/lib/test_fine_tuning_positional_arguments.py#L169)
preserve `test_method_list_events`,
`test_method_list_events_with_all_params`,
`test_raw_response_list_events`, `test_streaming_response_list_events`,
and
  `test_path_params_list_events`.

These retain the basic/all-parameter calls, parsed response types,
raw/streaming
response headers and close behavior, and empty-ID errors. The original
loose,
strict, and async aiohttp modes remain: **50 positional-call cases**,
alongside
the restored generated keyword-call examples.

Validation:

- Exact-source/AST proof for every retained method and parameterization;
both
  generated files match the public snapshot byte-for-byte.
- Pytest collection preserves all 50 original class/function/client-mode
IDs
after normalizing only the destination path, under both Pydantic
versions.
- `python -m pytest -n 0
tests/lib/test_fine_tuning_positional_arguments.py
  tests/api_resources/fine_tuning/jobs/test_checkpoints.py
tests/api_resources/fine_tuning/test_jobs.py`: **220 passed under
Pydantic v2
  and 220 under v1**, against the checked-in API mock.
- `./scripts/format` and `./scripts/lint` pass, including Ruff, Pyright,
mypy,
and import checks. Unrelated reporter-only formatting changes are
excluded.
- Verified public custom-code report: **40 → 38 mixed files**, exactly
these
two generated test customizations removed, and all other customizations
  unchanged.