Parallelize mesh and texture loading in client

[Azkellas]

This avoids loading multiple time a mesh if the gltf contains a lot of instancing.
Since we need to flatten the scene in the end for the global sdf, the gain is not that big but it's still a 3x speedup on a scene like the ABeautifulGame sample.
It's also a first step towards instance based sdf visualization and scene hierarchy.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.73%. Comparing base (390572c) to head (5018f1b).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #106   +/-   ##
=======================================
  Coverage   96.73%   96.73%           
=======================================
  Files          11       11           
  Lines        1778     1778           
=======================================
  Hits         1720     1720           
  Misses         58       58           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.