feat: optimize for reading a{sv} messages and headers

[bdraco]

closes #90

about 7% speed up.

The RPI3 can almost keep up with 4 adapters now. The python overhead downline is now more expensive after this PR so likely effort needs to shift back to bleak and HA.

[codecov]

Codecov Report

Base: 81.57% // Head: 81.72% // Increases project coverage by +0.15% 🎉

Coverage data is based on head (5717503) compared to base (2c6ee99).
Patch coverage: 94.11% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #98      +/-   ##
==========================================
+ Coverage   81.57%   81.72%   +0.15%     
==========================================
  Files          25       25              
  Lines        2941     2966      +25     
  Branches      567      573       +6     
==========================================
+ Hits         2399     2424      +25     
+ Misses        335      334       -1     
- Partials      207      208       +1     

Impacted Files	Coverage Δ
src/dbus_fast/__version__.py	0.00% <0.00%> (ø)
src/dbus_fast/_private/unmarshaller.py	96.45% <96.96%> (-0.05%)	⬇️
src/dbus_fast/message_bus.py	72.43% <0.00%> (-0.77%)	⬇️
src/dbus_fast/glib/message_bus.py	83.12% <0.00%> (+2.05%)	⬆️

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