ci: Compile Rust tests in release mode

[torokati44]

Let's see whether this is faster now...

Afterwards, I think it would still be favorable to create a custom Rust profile for CI, where optimizations are enabled, but debug checks are not disabled.

Also note that our cargo cache is primed with debug artifacts, so it's not trivial to accurately measure this.

[torokati44]

Current test times with empty cache:

With perfectly primed cache:

Cache sizes:
770, 770, 770, 550, 720 MB

With this PR, and empty cache:

With this PR, and perfectly primed cache:

Cache sizes:
580, 570, 650, 560, 490 MB

[torokati44]

After adding a new build profile, as follows:

[profile.ci]
inherits = "release"
opt-level = 2
debug-assertions = true
overflow-checks = true
incremental = true

For reference, we already had this:

[profile.release]
panic = "abort"

I get this on an empty cache:

And on a primed cache:

Cache sizes:
580, 650, 570, 570, 490 MB

While not 7, but still more than 6 minutes faster than the 22 minutes it is right now.