feat: speed up unmarshaller

[bdraco]

~4% speed up

[codecov]

Codecov Report

Base: 81.49% // Head: 81.68% // Increases project coverage by +0.19% 🎉

Coverage data is based on head (bd38f3e) compared to base (cde1893).
Patch coverage: 85.71% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #101      +/-   ##
==========================================
+ Coverage   81.49%   81.68%   +0.19%     
==========================================
  Files          25       25              
  Lines        2966     2971       +5     
  Branches      573      574       +1     
==========================================
+ Hits         2417     2427      +10     
+ Misses        338      335       -3     
+ Partials      211      209       -2     

Impacted Files	Coverage Δ
src/dbus_fast/__version__.py	0.00% <0.00%> (ø)
src/dbus_fast/_private/unmarshaller.py	96.52% <100.00%> (+0.06%)	⬆️
src/dbus_fast/signature.py	57.20% <100.00%> (ø)
src/dbus_fast/glib/message_bus.py	83.12% <0.00%> (+2.05%)	⬆️

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