Add BatteryLevel parse function

Author: colemancda

PluginSDK/Examples/BatteryLevel/Sources/BatteryLevel/Plugin.swift

@@ -0,0 +1,21 @@
+//
+//  Plugin.swift
+//  BatteryLevel
+//
+//  The only file a plugin author writes: a pure function from ParseInput to Fields.
+//  Decodes the GATT Battery Level characteristic (0x2A19), a single percentage byte.
+//
+
+import BLEPluginSDK
+
+func parseCharacteristic(_ input: ParseInput) -> Fields? {
+    // Routing already guarantees 0x2A19, but check so the plugin is correct standalone.
+    guard input.uuid?.assignedNumber16 == 0x2A19 else { return nil }
+
+    var payload = input.payload
+    guard let level = payload.readUInt8() else { return nil }
+
+    var fields = Fields(summary: "Battery")
+    fields.uint("level", label: "Battery Level", UInt64(level), unit: "%")
+    return fields
+}