Refactor variable names for consistency

[Will-Tyler]

Description

This pull request renames variables throughout the project for consistency and closes #165.

In general, the goal is to use the term "array" when referring to Zarr arrays and the term "field" in most other situations, as opposed to "column" or "variable".

In this pull request, I typically use the type of the Python object to determine an appropriate name. For example, I would name a Python variable that is a ZarrArraySpec instance array_spec. I determined the type of the objects by running the unit tests with the debugger. There are other locations in the code that refer to ZarrArraySpec instances as "fields" though—if desired, I can rename these as well for more consistency.

I also searched for uses of "var". In most cases, it seemed like "var" was used to mean "variant" and not "variable", so I left most of these alone.

Methods

I used regular expression searches to find the instances of the different terminology. For example, col[^umn] to find variables named something like col.

I used PyCharm's refactoring features to rename the Python variables.

Testing

I did not perform any testing of the changes. I am assuming that the unit tests will detect any issues.

[jeromekelleher]

Awesome, thanks @Will-Tyler! This is a big improvement 👍

Good to merge after rebase (can get this in or #252 first, it's up to you).

[coveralls]

coverage: 98.841% (-0.04%) from 98.884%
when pulling 74fa91b on Will-Tyler:issue-165
into 31a5935 on sgkit-dev:main.

[Will-Tyler]

#252 is merged now, and just rebased this branch!

[coveralls]

coverage: 98.843%. remained the same
when pulling 0dc6dea on Will-Tyler:issue-165
into d683a31 on sgkit-dev:main.

[coveralls]

coverage: 98.886% (+0.04%) from 98.843%
when pulling 0dc6dea on Will-Tyler:issue-165
into d683a31 on sgkit-dev:main.