Make fields/objects that don't change Immutable

[ghost]

Description:

This makes the fields of objects that don't change final it also prevents data-only objects from being mutable. Why does this matter? Mainly because objects with an unchangeable state are automatically thread-safe, and they don't suffer from weird state side effects.

It's worth noting that the thread-safe point only applies to objects containing fields that are 1) all immutable or 2) some that are mutable and the mutable fields aren't publicly accessible.

This is important as many of our tasks run async whilst using these objects.

Some objects simply hold data, and have no reason to be mutable, therefore:

• WorldCoord - Now an immutable object
• Coord - Now An immutable object

Also in many methods to reset a map we were using:
myMap = new HashMap<>();
This is not that efficient so it's been corrected to this:
myMap.clear();

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• I have tested this pull request for defects on a server.

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