[CI] ISAR conformance tests addition

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• Requested reviewers:

Reason why this change is needed

• To add ISAR conformance tests to IVAS conformance tests

Description of the change

• Replacing temporary file names with unique file names in tests/split_rendering/test_split_rendering.py, similar to the other tests
• Updates to gitlab-ci.yml file of ivas-conformance and ivas-conformance-linux to copy the split rendering reference vectors
• Updates to parse_commands.py to create Readme_IVAS_ISAR_dec.txt and Readme_IVAS_ISAR_post_rend.txt
• Updates to cleanup_26252.py and test_26252.py

Affected operating points

• CI only