Improve test-release CI job runtime

[danielocfb]

As we add more jobs and have existing ones perform more work, CI slows down. One of the main offenders is the 'test-release' job, which is found to have a both cold start runtime but also doesn't play particularly nice with our caching infrastructure. This has potential trickle down effects on other jobs, which may only get scheduled on runners once others have finished (because there exist overall limits on the number of runners in use), potentially delaying overall CI time doubly.
The slowness of this job seems to come down to two things: 1) our release builds use LTO etc., making linking a very lengthy
process
2) it turns out that release builds are not incremental by default [0],
causing a lot of recompilation to happen, despite our efforts of
caching intermediate artifacts

To fix these issues, we disable the link time optimization step in CI and enable incremental compilation. Doing so reduces runtime from >=3min down to ~1min.

[0] https://doc.rust-lang.org/cargo/reference/profiles.html#release

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.47%. Comparing base (99fc30a) to head (856651c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #954   +/-   ##
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  Coverage   94.47%   94.47%           
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  Files          57       57           
  Lines       10650    10650           
=======================================
  Hits        10062    10062           
  Misses        588      588           

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