Speed up the Hardware() constructor, and other optimizations

[dstndstn]

This is needed for some LSS optimization work: https://github.com/desihub/LSS/pull/101

• add a load_hardware_args() function that returns the arguments that should be passed to the Hardware() constructor -- useful when used with multiprocessing / pickle; and also returns the time validity range for that hardware configuration
• add a get_time_range kwarg to load_hardware() to return the datetime range when that hardware configuration is valid
• speeds up the Hardware() constructor, which was doing a 5000 x 5000 neighbor-search of positioners. Speed this up by argsorting on the X coordinate and using that to search only positioners in the X slice that could possibly be neighbors.

[dstndstn]

The unit tests are failing because https://github.com/desihub/desimodel/pull/170 is not merged yet

[araichoor]

sorry @dstndstn for the delay in reviewing! I had a look at the code, but it s a bit technical for me, so I fully trust you here :)

I ve done the following sanity check: rerun all the observed main survey with the main branch and with your pr460 branch: the outputs do exactly match, so perfect!

could you just:

• add the docstr documentation for the load_hardware_args() function?
• update the doc/changes.rst file? (you may need to rebase from main, as I updated this file since you submitted your PR).

then I ll merge it.

[dstndstn]

Okay, @araichoor , thanks for the checks! I added the things you mentioned (and a few other improvements!) Should be good to go!

[sbailey]

Thanks @dstndstn @araichoor. Merging now to include in the next tag.