Namely any CLI driven runtime-config fixtures such as,
- `--spawn-backend` and `start_method`,
- `--tpdb` and `debug_mode`,
- `--tpt-proto` and `tpt_protos`/`tpt_proto`,
- `reg_addr` as driven by the above.
This moves all fixtures and necessary hook funcs (CLI parsing,
configuring and test-gen) to the `._testing.pytest` module and thus
allows any dependent project to leverage these fixtures in their own
test suites after pointing to that plugin mod using,
```python
# conftest.py
pytest_plugins: tuple[str] = (
"tractor._testing.pytest",
)
```
Also, add a new `._testing.addr` helper mod which now contains
a factored `get_rando_addr()` helper for creating test-sesh unique
tpt-specific registry (or other) IPC endpoint addrs.
fe23331365