Correctly score pulse height tally when no cell filter is 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.

[paulromano]

Thanks @GuySten. I've made three refinements to improve code clarity and correctness:

• Eliminated code duplication in the SCORE_PULSE_HEIGHT case by consolidating the two branches into a single loop with a ternary operator for the cell index.
• Fixed a bug in tally_scoring.cpp where assigning to a mutable reference was inadvertently mutating model::pulse_height_cells, which could corrupt scoring for multiple pulse-height tallies. This now uses a const reference to safely bind either the filter's cells or the global vector.
• Changed pulse_height_cells from vector<int> to vector<int32_t> to match CellFilter::cells() for consistency.