We only encrypt fields if they don't match the placeholder value

We should add test coverage of this and we should care about the nullable aspect.

Ok, I added the tests to fix this, and they're now passing, so setting to "Needs review."

Note that I also updated the field type to "decimal" in the tests (it was "string" before, but since Drupal 10.2? decimal has its own type.)

I'd like to see a kernel test that proves this works for required fields... the only test we've changed is a unit test and that doesn't use a real database backend.

Just as a head up...

Given what I have found out in 🐛 Encrypted decimal field value not saved on drupal version 10.2.x+ Active where NULL is already inadvertently being returned by FieldEncryptProcessEntities::getUnencryptedPlaceholderValue for a decimal field, I am guessing changes would also need to be made to ProcessEntities::setEncryptedFieldValues for this not to be problematic.

Also based on 🐛 ProcessEntitiesTest is allowing unexpected results to slip through Needs work more testing beyond ProcessEntitiesTest is definitely need.

That said, I agree with the motivation behind this change.