[WIP/PoC] Add async testbench functions

[zyp]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 39.42308% with 63 lines in your changes are missing coverage. Please review.

Project coverage is 88.84%. Comparing base (7445760) to head (6faab6e).

Files	Patch %	Lines
amaranth/sim/core.py	43.37%	38 Missing and 9 partials ⚠️
amaranth/sim/_pycoro.py	15.78%	15 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #990      +/-   ##
==========================================
- Coverage   89.39%   88.84%   -0.56%     
==========================================
  Files          43       43              
  Lines        9516     9611      +95     
  Branches     2283     2302      +19     
==========================================
+ Hits         8507     8539      +32     
- Misses        820      874      +54     
- Partials      189      198       +9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[whitequark]

So I don't think we can really commit to this approach because it implements the new interface in terms of the old one and we want to deprecate and remove the old one. (We also want the new one to have less overhead, not more.)

[zyp]

I'm not intending to commit to this approach, but I think it'd be useful to prototype a simple working implementation first and write a suite of passing tests against it before starting on the «real» implementation.

[whitequark]

Yeah, no objection to that, of course.

[whitequark]

Thank you for this work, @zyp! PR #1344 supersedes this PR with a more complete implementation. We have ended up rewriting a lot of the simulator internals, as well as filling in the blanks in a few places where the RFC was unimplementable or underspecified.