Fix inf test ci

[2bndy5]

I'm guessing that the parallel writes to GITHUB_OUTPUT env var are causing the test CI to behave as if the workflow never finishes.

This patch, hopefully, should fix that by changing the env var's value to a temp file created during the test.

This also includes new clippy fixes using stable rust v1.87.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.55%. Comparing base (49a7c8d) to head (39f274c).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #140      +/-   ##
==========================================
- Coverage   97.58%   97.55%   -0.03%     
==========================================
  Files          14       14              
  Lines        3430     3435       +5     
==========================================
+ Hits         3347     3351       +4     
- Misses         83       84       +1     

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[2bndy5]

The test CI is still running indefinitely. even though it has finished all the steps. I'm going to have to raise this issue with GitHub itself.