bledev.hid: BLE keyboards and gamepads into events, both ways

[bdbarnett]

BLE keyboards, remotes and gamepads now feed events and keys the way USB ones do through usbif, and a board can be a BLE keyboard and gamepad itself. Stacked on #81 (bledev-host).

• bledev.hidreport: a HID report-descriptor parser and decoder with no Bluetooth in it. Keyboard events match usbif's boot-keyboard decoder event for event (3,000 random reports compared in the tests).
• bledev.hid: the HOGP host (reads the Report Map, pairs when the device asks, subscribes to every input report) and a peripheral serving a keyboard, consumer control and gamepad, with its identity derived from which of those it offers.
• The contract gains descriptors, encrypted characteristics, Connection.pair() and a long_read capability; fake, mpble and bleak implement them. Two mpble MTU bugs fixed on the way (the board as central to a peripheral that exchanges first).

The guide is the new section in docs/bledev.md; how it works and what it found is docs/bledev-internals.md, "How HID gets there".

Gates

• Parser vectors (the HID spec's boot keyboard, ESP32-BLE-Keyboard, CircuitPython's consumer control, adafruit_ble's map and gamepad, the Xbox Series BLE controller): pass on CPython, unix micropython and the P4. Each of six planted faults fails them.
• Fake radio end to end, on both interpreters: pass. Each of four planted faults fails it.
• Board to board over the air, both role directions (LCD-7 and T-Embed, and the P4 with the LCD-7): 112 of 112 events and the typed text exact, and a planted lost Shift fails. The one exception is the P4 as host, which loses reports below Python (P4 as BLE central loses notifications below MicroPython when Python is busy #87). The S3s never lost one.
• Pairing and bonding, both directions: the first connect pairs "just works" and bonds. Reconnecting after both boards reset reuses the stored keys. A host that lost its keys re-pairs. A host that won't pair can't read an encrypted device.
• Latency, as a key-press round trip: median 68-70 ms at the default interval and 29-30 ms at 7.5-15 ms, so roughly 35 and 15 ms one way. Decoding adds 1.7-2.8 ms.
• Laptop (bleak) host against the P4 under a vendor UUID, since Windows hides 0x1812 from apps: 112 of 112, and the plant fails.
• bless works as a laptop peripheral, with workarounds (see bless_peripheral.py).

All the numbers are in docs/bledev-internals.md, "HID, board to board and from the laptop".