tools/python/3.10: Set rpath when building to install/lib dir

This fix is necessary because venv will not use the Axii-installed shim, but will directly use the underlying Python executable. Without this, runtime linker errors will occur:

python: error while loading shared libraries: libpython3.10.so.1.0: cannot open shared object file: No such file or directory

This was still needed in addition to everything else mentioned in #362 (closed)