Add a CI check to keep the Python APIView parser version synchronized with APIView

## Problem

The `apiview-stub-generator` version used to generate Python APIView token files can differ from the parser version configured for Python in APIView. This produces token files whose hashes do not match the approved APIView revisions and makes release failures difficult to diagnose.

We recently observed the following:

1. APIView was configured to use `apiview-stub-generator` 0.3.28 for Python.
2. `azure-sdk-for-python/eng/apiview_reqs.txt` pinned `apiview-stub-generator` 0.3.31.
3. The Python release pipeline ran the `apistub` check through the in-repository `azpysdk` tooling. That tooling installed `eng/apiview_reqs.txt` and generated a token file using 0.3.31.
4. The generated token file did not hash to the approved APIView revision, which had been produced with 0.3.28.
5. When APIView processed the token file, it detected that its parser version differed and initiated regeneration using its configured 0.3.28 version.
6. Several minutes later, APIView replaced the token file with one whose hash matched the approved revision.

The delayed regeneration obscured the parser mismatch and contributed to an initial misdiagnosis. During the delay, the release appeared to be using an unapproved API surface even though the underlying API had already been approved.

## Current Python CI path

The SDK pipeline runs `eng/scripts/dispatch_checks.py` with `--checks="apistub"`. The `apistub` implementation in `eng/tools/azure-sdk-tools/azpysdk/apistub.py` installs the dependencies pinned in `eng/apiview_reqs.txt`, including `apiview-stub-generator`, before generating the Python token file.

The generated token file is subsequently submitted to `apiview.dev/autoreview` by `eng/common/scripts/Create-APIReview.ps1`.

## Proposed change

Add a required CI check that runs whenever `eng/apiview_reqs.txt` changes. The check should:

1. Read the pinned `apiview-stub-generator` version from `eng/apiview_reqs.txt`.
2. Read `ApiStubVersion` from `eng/pipelines/apiview-review-gen-python.yml` in `Azure/azure-sdk-tools`. This is the version installed by the Python APIView token regeneration pipeline.
3. Read `PythonLanguageService.VersionString` from `src/dotnet/APIView/APIViewWeb/Languages/PythonLanguageService.cs` in `Azure/azure-sdk-tools`. This is the parser version APIView expects for Python reviews.
4. Fail with a clear error unless all three versions match.
5. Report all three versions and explain that APIView must be updated and deployed before the Python dependency pin can be merged.

This check should prevent `azure-sdk-for-python` from moving to a parser version that APIView is not yet using.

## Required update sequence

Parser upgrades should occur in this order:

1. Release the new `apiview-stub-generator` version from `azure-sdk-tools`.
2. Update the Python parser version in APIView and deploy APIView.
3. Update `eng/apiview_reqs.txt` in `azure-sdk-for-python`.

APIView must be updated first because it can automatically regenerate token files using its configured parser version. Updating the Python repository first creates a window where locally generated tokens and APIView-generated tokens differ.

## Acceptance criteria

- A change to `apiview_reqs.txt` in the `azure-sdk-for-python` repository triggers the synchronization check.
- CI reads `ApiStubVersion` from `Azure/azure-sdk-tools/eng/pipelines/apiview-review-gen-python.yml`.
- CI reads `PythonLanguageService.VersionString` from `Azure/azure-sdk-tools/src/dotnet/APIView/APIViewWeb/Languages/PythonLanguageService.cs`.
- CI passes only when both `azure-sdk-tools` versions exactly match the version pinned in `eng/apiview_reqs.txt`.
- A mismatch fails before package release steps and displays all three versions and their source locations.
- The failure message documents the required update order.
- The check itself does not initiate or wait for an APIView parser upgrade.

## Version sources

The synchronization check compares these values:

| Repository | File | Value |
|---|---|---|
| `Azure/azure-sdk-for-python` | `eng/apiview_reqs.txt` | `apiview-stub-generator==` |
| `Azure/azure-sdk-tools` | `eng/pipelines/apiview-review-gen-python.yml` | `ApiStubVersion: ''` |
| `Azure/azure-sdk-tools` | `src/dotnet/APIView/APIViewWeb/Languages/PythonLanguageService.cs` | `VersionString { get; } = ""` |

The check should read the `azure-sdk-tools` files from its default branch. Passing the source check confirms that the coordinated APIView change has merged; the documented update sequence must still require APIView deployment before the `azure-sdk-for-python` update is merged.