Allow looking up ophyd-async device vectors by dotted name

[canismarko]

Devices can be retrieved either by their fully qualified name (e.g. detector-driver-acquire_time), or by dotted name (detector.driver.acquire_time).

Ophyd-async introduces device vectors, where square brackets are used to indicate each device in the vector. E.g. detector.overlay.overlays[0]. This currently does not work for ophyd-registry because it does not properly parse the square brackets. Shouldn't be too hard to add.