[Device]: K850 keyboard support

### Pre-flight checklist

- [x] I quit **Logi Options+** before testing.
- [x] I searched existing issues for my device.

### Device model

K850 keyboard

### Connection

Bluetooth (direct, no receiver)

### What's the problem?

Device is not detected at all

### `openlogi list` output

```text
MX Master 3S (—, vid=046d pid=b034)
└─ slot 255 ● MX Master 3S (mouse, wpid=?, battery=75% full (discharging))
model_ids=[b034,0000,0000] ext=0d serial=2534ZAP7RJK8 unit_id=22e8bc46 transports=btle

Keyboard K850 (—, vid=046d pid=b34d)
└─ slot 255 ● K850 Performance Wireless Keyboard (keyboard, wpid=?, battery=50% good (discharging))
model_ids=[b34d,4062,0000] ext=00 serial=— unit_id=b70ba500 transports=equad+btle

Cameras (1 Logitech UVC)
└─ ● Logitech BRIO (camera, vid=046d pid=085e, up to 4096x2160@30, id=0x1243400046d085e)
```

### `openlogi diag features` output

```text
device: K850 Performance Wireless Keyboard (direct 046d:b34d)
dump failed: device at index 0xff did not respond to HID++

device: MX Master 3S (direct 046d:b034)
idx id ver
0 0x0000 v2
1 0x0001 v2
2 0x0003 v4
3 0x0005 v0
4 0x1d4b v0
5 0x0020 v0
6 0x0021 v1
7 0x0007 v0
8 0x1004 v3
9 0x1b04 v5
10 0x1814 v1
11 0x1815 v2
12 0x2250 v1
13 0x2201 v2
14 0x2110 v0
15 0x2121 v1
16 0x2150 v0
17 0x2251 v0
18 0x00c3 v0
19 0x1802 v0
20 0x1803 v0
21 0x1806 v8
22 0x1816 v0
23 0x1805 v0
24 0x1830 v0
25 0x1891 v7
26 0x18a1 v0
27 0x1e00 v0
28 0x1e02 v0
29 0x1602 v0
30 0x1eb0 v0
31 0x1861 v1
32 0x9300 v0
33 0x9001 v0
34 0x1e22 v0
35 0x9203 v0
36 0x9205 v0
(37 feature entries)
```

### Details

The device can work both with BT and logitech unifying dongle. I can support you as much as you need.

Start by reproducing the reported behavior with `openlogi list` and `openlogi diag features`, comparing the K850 output with the MX Master 3S output. Trace the existing device-support entry points that handle HID++ discovery and feature diagnostics; done means the K850 is supported and its diagnostics no longer fail to respond.

Written by the indexing model from the issue text.