feat: speed up unmarshaller

[bdraco]

This is ~8% speed up

[codecov]

Codecov Report

Base: 81.20% // Head: 81.26% // Increases project coverage by +0.06% 🎉

Coverage data is based on head (1caadb7) compared to base (e07e281).
Patch coverage: 66.66% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
+ Coverage   81.20%   81.26%   +0.06%     
==========================================
  Files          26       26              
  Lines        3000     2999       -1     
  Branches      582      582              
==========================================
+ Hits         2436     2437       +1     
+ Misses        348      347       -1     
+ Partials      216      215       -1     

Impacted Files	Coverage Δ
src/dbus_fast/__version__.py	0.00% <0.00%> (ø)
src/dbus_fast/_private/unmarshaller.py	94.84% <100.00%> (-0.03%)	⬇️
src/dbus_fast/message_bus.py	71.37% <0.00%> (+0.37%)	⬆️

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