config: surface real make-uncompress failures, drop dead try/except

[jeffdi]

Summary

Fixes the silent-fallback bug in uncompress_gds() that caused chipfoundry/cf-cli#20 to look like an LFS bug when it wasn't. The previous implementation called subprocess.run without check=True so its except CalledProcessError block was dead code, and stderr/stdout went into PIPE and were thrown away. When make uncompress failed (e.g. on Fargate under disk pressure for a large repo) cf-precheck silently swallowed the real error and emitted only the misleading downstream [CRITICAL] A single valid GDS was not found message.

Behavior

After running make uncompress, judge by post-condition (presence of gds/*.gds files in the working tree) since caravel-lite's Makefile legitimately exits non-zero on the mag/ step after the gds/ step succeeds — failing the whole precheck on that benign mag-step exit would be wrong.

• gds/*.gds present → log INFO with the produced file list and the make exit code, and continue (works for both exit 0 and benign exit 2).
• gds/*.gds absent and make exited non-zero → log CRITICAL with returncode, stderr tail (4000 chars), stdout tail (200 chars). Exit 252.
• gds/*.gds absent and make exited zero → log CRITICAL "make uncompress reported success but produced no gds/*.gds files". Exit 252.
• gds/ directory missing entirely → log CRITICAL. Exit 252.

Per .cursor/rules/no-fallback-code.mdc.

Test plan

• Unit test mocking subprocess.run for all 4 branches (success-with-mag-noise, real-failure, success-with-no-output, missing-dir): pytest tests/test_uncompress_gds.py -v — 4/4 pass.
• Dev validation: built dev runner image with this branch, ran one-shot Fargate task against vyges/vyges-edge-sensor-soc@main (the repo in Precheck reporting SPDX exceptions for binary files #20). cf-precheck completed normally and wrote precheck_results/.../precheck.log instead of bailing in 501 ms. CloudWatch shows make uncompress produced 9 gds/*.gds file(s) ... INFO line and no CRITICAL.
• Prod validation after merge: trigger a remote precheck on a project that previously hit the silent failure and confirm either success or a clear, surfaced make uncompress failed (exit N) message.

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