feat(ble): add a NimBLE provider and fold its controls into Settings

Bluedroid cannot initialize beside the Lua runtime on this heap, so the
provider is NimBLE-Arduino. Scans keep the six strongest devices in a fixed
buffer rather than growing one. The standalone BLE app is gone: it was a
screen of toggles that belongs next to the other device settings.

test/ble.lua

@@ -0,0 +1,37 @@
+-- Run: lua test/ble.lua
+package.path = "sdcard/.lua/lib/?.lua;test/?.lua;" .. package.path
+
+local device = require("fake_device")
+device.bleDevices = {{name = "Sensor", address = "aa:bb:cc:dd:ee:ff", rssi = -42}}
+device.install()
+
+dofile("sdcard/.lua/apps/Settings/main.lua")
+
+init()
+device.tap("BLE")
+assert(device.labelled("off"))
+assert(not device.find("disconnect"))
+
+device.tap("turn on")
+assert(device.bleName == "Slate32 BLE")
+device.tap("scan devices")
+assert(device.labelled("scanning BLE"))
+tick()
+assert(device.labelled("Sensor"))
+
+device.tap("Sensor")
+assert(device.labelled("connecting BLE"))
+tick()
+assert(device.bleConnected == "aa:bb:cc:dd:ee:ff")
+assert(device.find("disconnect"))
+
+device.tap("disconnect")
+device.tap("start advertising")
+assert(device.bleAdvertising == "Slate32 BLE")
+device.tap("stop advertising")
+assert(device.bleAdvertising == nil)
+
+device.tap("turn off")
+assert(not device.bleInitialized)
+
+print("ok")