Store Manager::adapters() in OnceCell

[lukipuki]

Summary
Call to Manager::adapters() spawns a new never-ending thread, so we have to call it just once.

Related Issues
#83

Proposed Changes

• Use OnceCell to store Manager::adapters()

Checklist

• Tests pass locally
• Documentation updated if needed

[andrewdavidmackenzie]

The API to build_ble_stream

seems to have changed, but I don't see it in this PR...

I get this build error switching to this branch

error[E0283]: type annotations needed
   --> src/device_subscription.rs:211:9
    |
211 |         utils::stream::build_ble_stream(&device.mac_address.into(), Duration::from_secs(4)).await?;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                     ---- type must be known at this point
    |         |
    |         cannot infer type of the type parameter `B` declared on the function `build_ble_stream`
    |
    = note: multiple `impl`s satisfying `_: From<btleplug::api::bdaddr::BDAddr>` found in the following crates: `btleplug`, `meshtastic`:
            - impl From<btleplug::api::bdaddr::BDAddr> for BleId;
            - impl From<btleplug::api::bdaddr::BDAddr> for u64;
    = note: required for `btleplug::api::bdaddr::BDAddr` to implement `Into<_>`
help: consider specifying the generic argument
    |
211 |         utils::stream::build_ble_stream::<&T>(&device.mac_address.into(), Duration::from_secs(4)).await?;
    |                                        ++++++

[andrewdavidmackenzie]

Able to fix it relatively easy, but commenting in case you want to mention API change or take into account in semver version numbering

[andrewdavidmackenzie]

It seems to fix the problem and the thread count for my app is now stable over time.
Thanks!

[lukipuki]

Thanks for testing!

The API was changed in this recent PR: #76
It doesn't require a mention in release notes and changelog, as this is a change of unstable API that was not yet part of a release.

Btw, we don't have a changelog for this crate, I'll create one and make the release this week.