Fix build backend to use setuptools.build_meta

setuptools.backends.legacy is not available in older pip environments;
switch to the standard setuptools.build_meta and add wheel to requires.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -1,6 +1,6 @@
 [build-system]
-requires = ["setuptools>=68"]
-build-backend = "setuptools.backends.legacy:build"
+requires = ["setuptools>=68", "wheel"]
+build-backend = "setuptools.build_meta"
 
 [project]
 name = "ableton-osc"