-Add function to handle concatenating leak_i variables.
-Drop variables from housekeeping dataset that aren't needed
 for the CDF product.
-Update dimensions and add attributes to the housekeeping Dataset.
-Delete create_datasets function since packet_file_to_datasets.
 creates xarray datasets and those just need to be updated. This
 will happen in housekeeping and science data processing functions.
-Add function to process science data (WIP).
-Clean up code and add/update docstrings and comments.

hit_l1a.py was refactored to use the packet_file_to_datasets
function. The unit tests were updated to reflect changes.

-Added new fixtures for attributes manager, datasets dict, and
 housekeeping dataset.
-Added new tests for new functions (concatenating leak_i data
 and processing housekeeping).
-Added additional assertions for housekeeping dataset.

…ses, but only after hit_l1b is refactored not to use it

…he data arrays

… leak_i variables to assign as a dimension. Also change dims to a dict from a list since assign_coords takes in a dictionary

…er. Also add assertion to check values are correct