Implement RFC 73: Stricter connections.

[zyp]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.28%. Comparing base (638edff) to head (b07ee84).

Files with missing lines	Patch %	Lines
amaranth/lib/enum.py	33.33%	1 Missing and 1 partial ⚠️
amaranth/lib/wiring.py	90.90%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1637      +/-   ##
==========================================
- Coverage   91.28%   91.28%   -0.01%     
==========================================
  Files          44       44              
  Lines       11471    11493      +22     
  Branches     2236     2240       +4     
==========================================
+ Hits        10471    10491      +20     
- Misses        837      839       +2     
  Partials      163      163              

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[whitequark]

Needs at the very least:

• Tests for changes in lib.data and lib.enum
• Changelog update