Simplifying detection efficiency validation notebook.

[astronomerritt]

The notebook demonstrating the fading function/detection efficiency had a lot of extraneous code and while-loops instead of array operations, and was also missing an explanation of the fading function. I had to edit it anyway to make plots for the paper, so figured I may as well overhaul it while I was there.

Review Checklist for Source Code Changes

• [x] Does pip install still work?
• [x] Have you written a unit test for any new functions?
• [x] Do all the units tests run successfully?
• [x] Does Sorcha run successfully on a test set of input files/databases?
• [x] Have you used black on the files you have updated to confirm python programming style guide enforcement?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.14%. Comparing base (c2b800c) to head (59c9f77). Report is 27 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1035 +/- ## ========================================== + Coverage 80.90% 81.14% +0.23% ========================================== Files 70 70 Lines 3148 3166 +18 ========================================== + Hits 2547 2569 +22 + Misses 601 597 -4 ```

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