Retrieve a ScanNumber from numtracker and store it in the RunEngine persistent state dictionary

[callumforrester]

See expected sequence diagram: DiamondLightSource/dodal#991 (comment)

It is possible to pass a callback into the RunEngine constructor called scan_id_source. For every new run the RunEngine updates its internal state with a scan number, see docs. The default scan ID source is just an incrementing, in-memory value. The RunEngine's current scan ID can be found via RE.md["scan_id"].

For the above issue we need start sourcing IDs from numtracker. So this issue consists of writing a scan ID source function that retrieves a new ID and hooks it into the RunEngine.

Still TBD is the fallback behaviour if blueapi can't connect to numtracker and the default behavoir in a dev environment.

Acceptance Criteria

• There is a function that can retrieve a new scan number from numtracker
• It is passed to the RunEngine as scan_id_source
• ...