Fix non-deterministic python compilation

This CL fixes timestamps for zip entries to a hardcoded value to ensure
deterministic zip archives across checkouts, not just for incremental builds.
The value chosen for the fixed date is the same as the one used by soong_zip.

Bug: b/322788229
Test: Ran a few builds and verified that mdate for zipped files are
fixed as well as the generated zip files have identical hashes.

Change-Id: I3cd6fcf559d4d83d8813c93319b46e267ae64a2b