Make cross type conversions implicit

[mborland]

Closes: #400

[codecov]

Codecov Report

❌ Patch coverage is 99.02439% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.19%. Comparing base (e6e59c0) to head (7e5ae9f).
⚠️ Report is 13 commits behind head on develop.

Files with missing lines	Patch %	Lines
test/test_cross_type_assign.cpp	98.51%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #401      +/-   ##
===========================================
+ Coverage    96.10%   96.19%   +0.08%     
===========================================
  Files           71       72       +1     
  Lines         6109     6306     +197     
  Branches      2045     2124      +79     
===========================================
+ Hits          5871     6066     +195     
  Misses          34       34              
- Partials       204      206       +2     

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[cppalliance-bot]

An automated preview of the documentation is available at https://401.int128.prtest3.cppalliance.org/libs/int128/doc/html/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-05-12 18:04:07 UTC