Replace ChOp skipif with a fail-fast precomp

[arifthpe]

Replace the ChOp testing skipif with a precomp that exits with error if cloning or patching fails, rather than just skipping the test.

I think this is appropriate because we shouldn't have very frequent failures now that we have cached reference repos to clone with, so we can lean towards not silencing an issue.

All differences between new precomp and old skipif:

• Uses reference repo at standard path for cloning if available.
• Exits with error on failed commands (set -e), rather than skipping test.
• Output is direct to stdout and stderr rather than redirecting to a log file.
• Increased verbosity with set -x.

[reviewer info placeholder]

Testing:

• ChOp tests in ./util/cron/test-gpu-ex-cuda-12.ofi.bash config pass