Add py_deps aspect and deps requirements rule

chore: downgrade rules_python

feat: add rust toolchain to packages based on required build backend

fix: add path to imports

fix: use Windows paths as POSIX

feat: add ppc cpu remapping

fix: remove coverage tool usage from the host Python reference

fix: pathsep on Windows and Bazel v9

feat: drop symbolic links requirement

feat: add last_rc testing