Numtracker client passes user supplied visit directly

## Steps To Reproduce
1. Run blueapi using system test config (with services running)
2. Run a scan using `cm12345-6", sub: "foo` as the visit, eg
```shell
blueapi -c tests/system_tests/config.yaml controller run -i 'cm12345-6", sub: "foo' spec_scan '{"detectors":["det"], "spec":{"axis": "stage.x", "start": 1.0, "stop": 8.0, "num": 8, "type": "Line"}}'
```
3. See that numtracker was queried for the given subdirectory

At the moment it doesn't really affect anything because the scan file path returned from numtracker is not used anywhere but if it ever is, we should probably validate the visit.