Revert "Use setuptools"

This reverts commit d3053ce.

Author: Pierre-Sassoulas

pyproject.toml

@@ -62,8 +62,8 @@ sphinx = "*"
 sphinx-autobuild = "*"
 
 [build-system]
-build-backend = "setuptools.build_meta"
-requires = [ "setuptools>=77" ]
+requires = ["poetry-core>=2.2.1"]
+build-backend = "poetry.core.masonry.api"
 
 [tool.ruff]
 line-length = 120