Implement RFC 59: Get rid of upwards propagation of clock domains

[wanda-phi]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 89.79%. Comparing base (09d5540) to head (6958730).

Files	Patch %	Lines
amaranth/hdl/_ir.py	88.88%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1259      +/-   ##
==========================================
+ Coverage   89.78%   89.79%   +0.01%     
==========================================
  Files          43       43              
  Lines       10055    10088      +33     
  Branches     2439     2450      +11     
==========================================
+ Hits         9028     9059      +31     
- Misses        830      832       +2     
  Partials      197      197              

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[whitequark]

Thanks!