Overhaul NotNull annotation usage

[theEvilReaper]

Proposed changes

We can enforce NotNull annotation by default using the package-info file. This way, all elements are considered non-null unless explicitly annotated as nullable. It improves readability by reducing redundant annotations and highlighting only the cases where null is actually allowed.

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• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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