Add time-of-flight beam

[toastisme]

This adds a time-of-flight beam object (TOFBeam) to dxtbx, to allow for neutron time-of-flight Laue experiments.

TOFBeam derives from Beam, and differs in that it has a sample_to_moderator_distance and does not have an explicit monochromatic wavelength. To satisfy the BeamBase interface it still has set_wavelength and set_s0 methods, which raise exceptions. This is a code smell, but is a trade off to prevent needing to modify the BeamBase interface and having dynamic casting downstream etc. The BeamBase get_wavelength and get_s0 methods are satisfied by allowing a TOFBeam to store a given reflection (only through required values to avoid dependency on DIALS), thereby giving it a wavelength and s0.

To account for multiple beam types a TOFBeamFactory has been added, which conforms to a general beam factory interface outlined in AbstractBeamFactory. BeamBaseFactory has also been added, which chooses between TOFBeamFactory BeamFactory based on input.

[codecov]

Codecov Report

Merging #492 (7e8dbd4) into main (c119306) will increase coverage by 0.16%.
The diff coverage is 67.22%.

@@            Coverage Diff             @@
##             main     #492      +/-   ##
==========================================
+ Coverage   40.91%   41.08%   +0.16%     
==========================================
  Files         176      176              
  Lines       15528    15619      +91     
  Branches     2795     2822      +27     
==========================================
+ Hits         6354     6417      +63     
- Misses       8618     8629      +11     
- Partials      556      573      +17     

[ndevenish]

@toastisme going to revisit this context shortly

[ndevenish]

Will recreate with newer versions of code.