feat: speed up marshalling headers

[bdraco]

This is a 22% speed up

closes #140

[codecov]

Codecov Report

Base: 81.70% // Head: 81.84% // Increases project coverage by +0.13% 🎉

Coverage data is based on head (647fb60) compared to base (d7d301c).
Patch coverage: 91.42% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #142      +/-   ##
==========================================
+ Coverage   81.70%   81.84%   +0.13%     
==========================================
  Files          27       27              
  Lines        3100     3106       +6     
  Branches      642      643       +1     
==========================================
+ Hits         2533     2542       +9     
  Misses        347      347              
+ Partials      220      217       -3     

Impacted Files	Coverage Δ
src/dbus_fast/__version__.py	0.00% <0.00%> (ø)
src/dbus_fast/_private/marshaller.py	95.77% <94.11%> (-1.29%)	⬇️
src/dbus_fast/glib/message_bus.py	82.37% <0.00%> (+2.04%)	⬆️

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[bdraco]

Tested in production 👍