feat(winrtble): implement add_peripheral (connect by address)

[tanarchytan]

What

Implement the WinRT Central::add_peripheral, which currently returns Err(NotSupported). It creates a Peripheral from the given PeripheralId the same way the scanner registers a discovered device, and returns an already-known entry if present. Also adds the symmetric From for BDAddr.

Why

add_peripheral was added to the Central trait in 0.12.0 for Android but left unimplemented on Windows. Without it, a device the OS already knows (bonded, or connected to another central such as a phone) cannot be reached on Windows unless it happens to be advertising. This brings WinRT to parity with Android: get a Peripheral by address, then call connect(), which already uses FromBluetoothAddressAsync.

Tested on hardware: connects to a bonded device that is connected to another central and is not advertising, then reads and writes its GATT.

[tanarchytan]

The failing linux check is not from this PR.

This branch only changes src/winrtble/adapter.rs and src/winrtble/peripheral.rs. The linux job fails in the clippy step (cargo clippy --all-features), and the one build-breaking error is in the bluez backend, which this PR does not touch:

error: this loop never actually loops
  --> src/bluez/peripheral.rs:144
  note: `#[deny(clippy::never_loop)]` on by default

That loop returns on its first iteration, so clippy's never_loop lint (deny by default) rejects it. It only shows up on linux because src/bluez is the Linux backend and the clippy step runs on every OS with --all-features. macOS (corebluetooth), android, and format all pass. windows is marked cancelled only because the matrix is fail-fast and linux failed first. There are no clippy errors in the winrtble files this PR changes.

This is pre-existing under newer stable clippy (1.96, edition 2024): the most recent Rust run on master is already failing the same way. I kept the bluez code untouched to keep the PR scoped to winrtble. Glad to rerun once it is sorted, or to send a separate one-line fix for src/bluez/peripheral.rs:144 (clippy gives a machine-applicable suggestion) if that would help.