Add `clash-cores:doctests` to GitLab CI

[DigitalBrains1]

Fixed minor details in clash-cores CRC core.

With multiple-hidden enabled, the following doctest line:

crcEngine' = exposeClockResetEnable crcEngine systemClockGen resetGen enableGen

worked fine on GHC 9.4.8 and 9.6.{4,5}. But on GHC 8.10.7, 9.0.2 and 9.2.8, GHC wanted to check WithSingleDomain then and there, but could not because the crc term to crcEngine could not be inspected through TryDomain. The GHC's where it did work postponed this check to the myEngine binding in the next doctest line, where it could be resolved.

However, this exposeClockResetEnable is superfluous anyway as the sampleN function later on deals with such implicit parameters fine on its own. So the code is changed to no longer use exposeClockResetEnable and instead specify the domain to sampleN.

Additionally, a function for which no documentation was even generated had Haddock documentation on a constraint. Haddock on GHC 8.10.7 cannot handle this, breaking the doctests for clash-cores.

The documentation of that constraint has simply been removed.

With these details fixed, we can run clash-cores:doctests in GitLab CI. Up until now, we only ran it for external PR's in the GitHub CI Build and Test job, which was an accidental disparity.

GitHub CI also received several correctness and performance tweaks.

Still TODO:

• Write a changelog entry (see changelog/README.md)
• [x] Check copyright notices are up to date in edited files (did not add copyright for minuscule changes)

[DigitalBrains1]

I should take a look at CI for 1.8 to see if the tweaks here also make sense there.