Pulse height does not score over whole geometry when no cell filter present.

[GuySten]

Description

Currently when no CellFilter is specified, pulse height tally results are always 0.
This PR fix that and now when no cell filter is specified, all the geometry is scored to.

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 15) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[cfichtlscherer]

Thanks for your work again. I am not sure if we need this. Why would you want to know the pulse-height over the entire geometry when no CellFilter is provided?

[GuySten]

I discovered this unexpected behavior while trying to test a simple example containing one cell.

This can be useful for example when you have a model of one cell that is the detector vacuum boundary conditions and a fixed source.
You should be able to tally the pulse spectrum over the whole geometry (the detector) and you can model the difference between large and small detectors by changing the cell dimensions.

Now you have to specifiy a cell filter with that one cell as a workaround.

[vitmog]

Each filter must have the default "neutral" form $f(x) \equiv 1$. Otherwise, it would be necessary to define all available filters for each detector.