Android: Fix crash in handleDroppedPeers

[ovitrif]

Fixes synonymdev/bitkit#2133

(Android-only) Fix to avoid ConcurrentModificationException while addedPeers list is modified from other thread.

Former setup:

1. Scheduling was done using TimerTask which creates a different thread each time it's invoked
2. Since we also change addedPeers from react-native, there was a chance to get into this issue especially at app start, when both the react-native code as well as the native LDKModule code would mutate the same list.

Fix:
Use a thread-safe mutable list implementation, I picked ConcurrentLinkedQueue because it's less resource-consuming than other options.

Extra:
Rewrote the implementation of the scheduled repeating task, to use more performant and adequate APIs which actually wait for the scheduled work to finish, then delay the next execution with 3 seconds.

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