Make Zarr optional for testing

[mavaylon1]

Motivation

What was the reasoning behind this change? Please explain the changes briefly.

After discussions with the team, we decided to have the zarr be an optional dependency.

How to test the behavior?

Show how to reproduce the new behavior (can be a bug fix or a new feature)

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.84%. Comparing base (8917eaf) to head (83defba).
Report is 29 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1141      +/-   ##
==========================================
+ Coverage   88.78%   88.84%   +0.05%     
==========================================
  Files          45       45              
  Lines        9782     9786       +4     
  Branches     2778     2778              
==========================================
+ Hits         8685     8694       +9     
+ Misses        780      776       -4     
+ Partials      317      316       -1     

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[mavaylon1]

@rly We don't currently cover the else statement in append data. The gap in this PR is the same else statment, but under the zarr conditional. Are you okay with this gap in coverage for now?

[mavaylon1]

@rly made a simple example. It has full coverage and covers the missing spot I mentioned from prior to this PR. It's not a actual iterable class since it does not have iter or next, but I think it is fine.

[mavaylon1]

@stephprince done