Fix Linux wheel illegal-instruction crashes

[cjacoby-sptfy]

Summary

Fixes #454 by preventing Linux x86_64 wheels from accidentally requiring CPU instructions newer than the project’s documented baseline.

The manylinux build previously used -march=native. Because wheel builders may run on newer CPUs, this could compile host-specific instructions into the distributed wheel. On older CPUs, importing pedalboard could then terminate with SIGILL (Illegal instruction).

Changes

• Default Linux x86 builds to the AVX baseline using -mavx.
• Preserve native optimization as an explicit opt-in with USE_MARCH_NATIVE=1.
• Explicitly disable native optimization in wheel-building CI.
• Add a compatibility smoke test for manylinux x86_64 wheels under QEMU CPU models representing:
  • Intel Ivy Bridge
  • AMD EPYC Milan
• Verify that the installed wheel can import pedalboard and process audio with Gain.
• Document the Linux x86_64 AVX requirement.

Validation

Native GCP machines

The exact manylinux x86_64 wheels produced by this PR’s CI run were tested on native GCP VMs using:

• Intel Ivy Bridge
• AMD Milan

All CPython wheels from 3.10 through 3.15 successfully imported and processed audio on both machines: 12/12 passed.

As a negative control, the published pedalboard==0.9.21 CPython 3.11 wheel reproduced the original failure on both machines:

Illegal instruction (core dumped)
exit=132

This confirms that the test environments can detect the original incompatibility.

CI and local testing

• All 36 wheel-building CI jobs passed.
• The new QEMU compatibility check passed for CPython 3.10–3.15 manylinux x86_64 wheels.
• Full local Linux test suite:
  • 26,761 passed
  • 50 skipped

The only non-passing job in the CI run was the macOS Python 3.15 test job, which timed out after six hours. It did not report a test failure and does not exercise the Linux wheel-building path changed here.

[caravanuden]

looks good! just a couple questions

[tdhopper]

I reproduced the existing bug in docker and verified the changes resolve it.