MCAP: Replace latch with a synchronized() or lock

[jespersmith]

It seems that a countdown latch was used here instead of a simple lock. Adding a private final Object messagesLoadedLock = new Object(); and using synchronized(messagesLoadedLock) {} instead would avoid random nullptrexceptions due race conditions.

Same for chunckLoadedLatch.

simulation-construction-set-2/scs2-session-logger/src/main/java/us/ihmc/scs2/session/mcap/MCAPBufferedChunk.java

Line 346 in 6c0c6ec

messagesLoadedLatch.await();