iOS: parse and discard RSP_KEEPALIVE messages

cue-ios/CueIOS/AppState.swift

@@ -251,6 +251,9 @@ final class AppState {
         case .cellK(let k):
             calCellConstant = Double(k)
             status = String(format: "Device cell constant: %.4f cm\u{207B}\u{00B9}", k)
+
+        case .keepalive:
+            break
         }
     }
 

cue-ios/CueIOS/Models/Protocol.swift

@@ -29,6 +29,7 @@ let RSP_REF_FRAME:    UInt8 = 0x20
 let RSP_REF_LP_RANGE: UInt8 = 0x21
 let RSP_REFS_DONE:    UInt8 = 0x22
 let RSP_REF_STATUS:   UInt8 = 0x23
+let RSP_KEEPALIVE:    UInt8 = 0x50
 
 // Cue -> ESP32
 let CMD_SET_SWEEP:     UInt8 = 0x10
@@ -123,6 +124,7 @@ enum EisMessage {
     case refsDone
     case refStatus(hasRefs: Bool)
     case cellK(Float)
+    case keepalive
 }
 
 // MARK: - Response parser
@@ -254,6 +256,9 @@ func parseSysex(_ data: [UInt8]) -> EisMessage? {
     case RSP_CELL_K where p.count >= 5:
         return .cellK(decodeFloat(p, at: 0))
 
+    case RSP_KEEPALIVE:
+        return .keepalive
+
     default:
         return nil
     }