feat: improve performance of unmarshalling variants

[bdraco]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.48%. Comparing base (e1aaf0a) to head (b3640db).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #354      +/-   ##
==========================================
+ Coverage   83.41%   83.48%   +0.06%     
==========================================
  Files          28       28              
  Lines        3341     3354      +13     
  Branches      604      604              
==========================================
+ Hits         2787     2800      +13     
  Misses        346      346              
  Partials      208      208              

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[codspeed-hq]

CodSpeed Performance Report

Merging #354 will create unknown performance changes

_{Comparing unmarshall_var (b3640db) with main (e1aaf0a)}

Summary

🆕 3 new benchmarks

Benchmarks breakdown

	Benchmark	main	unmarshall_var	Change
🆕	test_marshall_bluez_get_managed_objects_message	N/A	73.2 µs	N/A
🆕	test_unmarshall_bluez_properties_message	N/A	45.5 µs	N/A
🆕	test_unmarshall_bluez_rssi_message	N/A	47.3 µs	N/A