Fix manually set default importances not printed

[MicahGale]

Pull Request Checklist for MontePy

Description

This fixes the bug where cells made from scratch almost never prints their importance in the output no matter if the importance were manually set (#892). Turns out that the parameter self._explicilty_set is set to True when the official setters are used, however, this value is never checked for formatting. To fix this was rather trivial.

However this issue brought up a question of behavior. In the test case cell.importance.all=1.0 is used on an unattached cell. It's assumed that this would set all importance. However, the documentation says that this only works on the particles in the problem. The code assumed that if the cell is not attached to a problem that cell.importance.all has no effect. This is rather intuitive. So I decided on the following behavior. Is this correct?

1. With no problem importance.all sets the importance for every (~37) particle types.
2. All particle importances are filtered first by problem.mode before printing. This is to avoid ~37 separate imp:X=1 clauses.

Finally, I noticed that in the tests for cell 4 only importance.neutron is set but the expected behavior is to print the default value for importance.photon. I decided to ignore this for now, and we can discuss.l

Fixes #892

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📚 Documentation preview 📚: https://montepy--921.org.readthedocs.build/en/921/

[tjlaboss]

Finally, I noticed that in the tests for cell 4 only importance.neutron is set but the expected behavior is to print the default value for importance.photon. I decided to ignore this for now, and we can discuss

Because the problem is in mode n p, then the photon importance needs to be printed as well.

[MicahGale]

So whenever any importance is set all importances for that cell should print?

[tjlaboss]

All importances for the problem mode should print*, else MCNP will error out with X entries not equal to number of cells = Y.

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*unless explicitly nullified for all cells, which is a feature that can be supported at a later date. See MCNP 6.3.1 Manual § 5.12.1:

Similarly, if an IMP: parameter appears on one cell card, a fatal error occurs if a
comparable entry does not appear on all cell card

[MicahGale]

SMH.

[tjlaboss]

7: See above