Decide on http client dependencies

Requests does not support async requests. Making numtracker integration async (ACQP-436) would need `httpx` and it'd make sense to only have one library.

`aiohttp` could also be an alternative but is async only so would require further changes where as httpx supports both so would be a drop in replacement.

## Acceptance Criteria
- There is one http library in use in blueapi
- That library can make async requests