[ViPPET] Add functional tests for performance job metadata flow

[ktaube26]

Description

Adds a new functional test module for the ViPPET performance job metadata flow (metadata_mode=file). The new test file covers the full end-to-end lifecycle of metadata collection during performance jobs, as well as the relevant error paths.

File added: tools/visual-pipeline-and-platform-evaluation-tool/vippet/tests/functional/test_performance_metadata_flow.py

The tests validate the following behaviours:

Happy path (@pytest.mark.full):

• A performance job submitted with metadata_mode=file on a pipeline that includes a gvametapublish element reaches COMPLETED state and includes a non-empty metadata_stream_urls dict in its status response.
• Each metadata snapshot endpoint (derived from the stream URL) returns HTTP 200 with a non-empty JSON array of records.
• Each metadata SSE stream endpoint returns HTTP 200 with Content-Type: text/event-stream.

Pipeline/variant combinations are discovered dynamically at collection time by querying the VIPPET API and filtering for variants whose pipeline graph contains a gvametapublish node. If none are found (e.g. no compatible device is available), the parametrized tests are automatically skipped with a descriptive reason.

Error paths (@pytest.mark.smoke / @pytest.mark.full):

• Metadata snapshot/stream requests for a non-existent job ID return 404.
• Metadata snapshot request for an existing job with metadata_mode=disabled returns 404 with a message that references metadata.
• A performance job submitted with metadata_mode=file on a pipeline without a gvametapublish element reaches FAILED state with an error referencing gvametapubl

Checklist:

• I agree to use the APACHE-2.0 license for my code changes.
• I have not introduced any 3rd party components incompatible with APACHE-2.0.
• I have not included any company confidential information, trade secret, password or security token.
• I have performed a self-review of my code.