build: add cross-compile support

[bernot-dev]

The build currently relies on QEMU emulation for arm64 builds (#346). This is slow.

This change uses Rust's ability to cross-compile for different platforms instead of relying on emulation, resulting in much faster builds.

Expected improvement is from ≈1h25m to <10m. Local cross-platform builds took about 3-7 minutes for me.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.9%. Comparing base (a2da58a) to head (a2f7d90).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #506   +/-   ##
=====================================
  Coverage   73.9%   73.9%           
=====================================
  Files         50      50           
  Lines       3911    3911           
=====================================
  Hits        2894    2894           
  Misses      1017    1017           

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

[bernot-dev]

After a bit of wrestling with dynamically linked libraries (back to musl), it's working now. I successfully build on amd64 for amd64 and arm64, and ran each image without arguments, resulting in the successful output of the help text in each case. This is sufficient to verify that compilation and linking completed successfully.

[jsuereth]

Thanks so much for the fixes!!!