fix: address type issue with NodeJS.Timer

this fix puts a flexible return time that works in both in browser and node environments

Author: rsdmike

src/core/AMTRedirector.ts

@@ -48,7 +48,7 @@ export class AMTRedirector implements ICommunicator {
   protocol: Protocol
   amtAccumulator: string
   amtSequence: number
-  amtKeepAliveTimer: NodeJS.Timeout | null
+  amtKeepAliveTimer: ReturnType<typeof setInterval> | null
 
   fileReader: FileReader
   fileReaderInUse: boolean