Refactor fit bragg peaks and add unit tests

[MialLewis]

Description of work:

Refactors the _fit_bragg_peaks portion of EVSCalibrationFit, making it easier to follow and unit test. This was probably the most convoluted function.

Unit tests have been added where the code has been refactored.

To test:
Review code.
Review test changes.
Ensure all automated tests pass.
Ensure the tests in test_system.py pass locally (You can run the system tests using python -m unittest discover -s ./unpackaged/vesuvio_calibration/tests/system from the root of the repository.) Note that test_fit_bragg_peaks_copper and test_fit_bragg_peaks_lead are unreliable and fail on different detectors on different PCs. Please post the stack trace if they fail on your machine.

[robertapplin]

Lots of new tests which is great 👍 I have a few code suggestions but feel free to push back if you disagree

[robertapplin]

I get one failure locally:

FAIL: test_fit_bragg_peaks_copper (test_system.TestEVSCalibrationFit)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\mlc47243\AppData\Local\mambaforge\envs\mantidnightly\lib\site-packages\mock\mock.py", line 1417, in patched
    return func(*newargs, **newkeywargs)
  File "C:\Users\mlc47243\Documents\mantid-dev\vesuvio\unpackaged\vesuvio_calibration\tests\system\test_system.py", line 374, in test_fit_bragg_peaks_copper
    self.assert_fitted_positions_match_expected(expected_values, params_table,
  File "C:\Users\mlc47243\Documents\mantid-dev\vesuvio\unpackaged\vesuvio_calibration\tests\system\test_system.py", line 474, in assert_fitted_positions_match_expected
    raise AssertionError(error_dict)
AssertionError: {'f3.LorentzPos': ['Element 15: Expected 11323.436309381943, found 4574.390063160628. atol 6749.0462462213145, rtol 1.4753980646674738,max tol: 0.1']}

is this expected?

[MialLewis]

Yes that's expected, going to let that failure go for now and fix in a later PR.

[robertapplin]

Thanks, happy to approve in that case 👍