Add the Cirrus40 keyboard

[schuay]

A 40% keyboard with focus on usable encoders. The PCB uses external pullups for encoder pins, hence the custom initialization logic.

https://github.com/schuay/cirrus40

Description

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[schuay]

Thanks for the quick review, applied.

[schuay]

By the way, why did you suggest removing LTO? Locally I set OPT ?= 2 and combine that with LTO. I certainly don't need size opts, and do want reasonable speed opts.

[drashna]

because, in general LTO is used primarily as a means for space savings. And short of using Quantum Painter and full on images, there is absolutely no shortage of space on RP2040's (1-16MB flash chips, and all).

Aside from that, additional optimizations aren't really going to gain you a lot.

And optimization is more likely to cause issues than be helpful here.

[schuay]

@drashna What is the remaining process to land this PR? Do you have more comments?

[schuay]

@zvecr thanks for the review, all requested changes applied. Please take a look again.