Update to PHPStan 2.x

[Firehed]

This fixes a few type risks along the way, and adds some of the remaining into the baseline. The majority of those added to the baseline are more-or-less expected errors around input validation where badly formatted input is expected to error or throw.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.33%. Comparing base (4231fc7) to head (537d0b0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #92      +/-   ##
============================================
+ Coverage     81.26%   81.33%   +0.06%     
- Complexity      308      311       +3     
============================================
  Files            33       33              
  Lines          1025     1034       +9     
============================================
+ Hits            833      841       +8     
- Misses          192      193       +1     

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