Remove Python tests ported to Go testscript framework
Removed tests now covered by Go integration tests:
- test_config.py: Entire file (1 test)
- test_run.py: 6 tests (kept 1 - TTY test requires pexpect)
- test_build.py: All 12 tests (file now placeholder)
- test_predict.py: 16 tests (kept 2 - async/mock server tests)
Removed 11 fixture directories now embedded in .txtar files:
- fast-build, many-inputs-project, overrides-project
- path-output-project, path-project, pipeline-project
- procedure-project, pydantic1-none, python-313
- string-list-project, string-project
Remaining Python fixtures (2):
- async-sleep-project (for test_concurrent_predictions)
- pipeline-requirements-project (for test_predict_pipeline_downloaded_requirements)
Simplified util.py to remove unused assert_versions_match function.
Python test count: 37 -> 3 (1 run + 2 predict)
Go test count: 60 -> 87 (+27 new tests)
