Investigate enabling validate_checksum as default True

[braingram]

Description of the problem

To address issues of data corruption (like the pre-commit whitespace stripping that held up: spacetelescope/romancal#1161) investigate enabling validate_checksum as default True.

If not already the behavior (I don't recall at the moment) the validation could occur only when the block is read (so a file opened with lazy_load=True and corrupt data would not raise an error until the corrupt array data is accessed). This may require some changes to how validate_checksum behaves and documentation updates. Depending on the impact of the change a deprecation period could be considered.