fix: re set ninja as default build backend for python except if AIDGE_BUILD_GEN is set in environment

Revert "feat : split the whole pyproject.toml back in multiple pieces as setuptools generates bugs when both are coexisting"

This reverts commit e653863d.

This reverts commit f982c0b7.

feat : split the whole pyproject.toml back in multiple pieces as setuptools generates bugs when both are coexisting