`characteristics()` and `services()` of `Peripheral` returning a `HashMap` instead of a `BTreeSet`

[hansmbakker]

Feature Description

Would it be possible to have characteristics() and services() of Peripheral return a HashMap instead of a BTreeSet?

That way, looping over the characteristics or calling iter().find() to find the characteristic you need is not needed anymore as below: https://github.com/deviceplug/btleplug/blob/76fd7956352fc59e35dc4e27d9de285df0554e43/examples/lights.rs#L63-L66

Instead you could do something like

let cmd_char = light.characteristics()[&LIGHT_CHARACTERISTIC_UUID];

[rib]

One thing to consider here is that bluetooth le peripherals may advertise multiple instances of a service or characteristic with the same Uuid (differentiated by their underlying AT handle) which couldn't be supported by btleplug if they were only exposed via a HashMap, indexed by uuid.

Their on-device order may also be significant, which would be lost with a HashMap.

[thomaseizinger]

let cmd_char = light.characteristics()[&LIGHT_CHARACTERISTIC_UUID];

If it is just about API ergonomics, then a new type around the returned BTreeSet plus an imlementation of Index would also allow this API.