- ci only: use a separate zig cache dir for each run
- use `tools/bazel` everywhere.
- remove arm64 tests. They don't give enough value to be worth the
brittle environment.
- remove windows execution, except for launcher. Ditto. I will probably
bring them back.
This removes all other Bazel test commands, so all tests can be again
tested with `bazel test ...`.
Also, fixes linux-arm64 glibc tests. Until now they've worked only in
CI. Now they work everywhere I tried.
