Add helper functions for measuring and comparing distributions

[sethrj]

This is to be used for understanding physics distributions (e.g. exiting polar angle) and for robustness against future refactors. Caveats:

• The classes were generated with the help of Copilot.
• I think the distribution comparison tests are wrong; the goal is to estimate the mean and variance of the underlying distribution, and to estimate how good that estimate is (variance of the variance?), and to be able to make comparisons based on those.
• This class itself could use tests.
• It may also belong in the main codebase rather than inside /test.
• We should consider using/requiring boost or another lighter library with statistics support to do the actual confidence tests.

[github-actions]

Test summary

 4 050 files   6 202 suites   4m 23s ⏱️
 1 433 tests  1 425 ✅  8 💤 0 ❌
19 901 runs  19 827 ✅ 74 💤 0 ❌

Results for commit 7c0ed51.

♻️ This comment has been updated with latest results.