Misc. Cleanups

[rlizzo]

Motivation and Context

Why is this change required? What problem does it solve?:

cleaned up checks for suitable user keys. improved test coverage, made remote tests run faster

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Documentation update
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Is this PR ready for review, or a work in progress?

• Ready for review
• Work in progress

How Has This Been Tested?

Put an x in the boxes that apply:

• Current tests cover modifications made
• New tests have been added to the test suite
• Modifications were made to existing tests to support these changes
• Tests may be needed, but they are not included when the PR was proposed
• I don't know. Help!

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have signed (or will sign when prompted) the tensorwork CLA.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #151 into master will increase coverage by 0.17%.
The diff coverage is 98.4%.

@@            Coverage Diff            @@
##           master    #151      +/-   ##
=========================================
+ Coverage   94.83%     95%   +0.17%     
=========================================
  Files          63      63              
  Lines       11145   11203      +58     
  Branches      996     998       +2     
=========================================
+ Hits        10569   10643      +74     
+ Misses        387     372      -15     
+ Partials      189     188       -1

Impacted Files	Coverage Δ
src/hangar/records/parsing.py	98.51% <ø> (-0.01%)	⬇️
tests/test_remotes.py	98.52% <100%> (+0.01%)	⬆️
tests/test_metadata.py	100% <100%> (ø)	⬆️
tests/test_utils.py	100% <100%> (ø)	⬆️
src/hangar/context.py	93.04% <100%> (ø)	⬆️
src/hangar/arrayset.py	95.52% <100%> (ø)	⬆️
src/hangar/backends/hdf5_00.py	93.7% <100%> (ø)	⬆️
tests/test_arrayset.py	100% <100%> (ø)	⬆️
src/hangar/repository.py	97.6% <100%> (ø)	⬆️
tests/test_merging.py	100% <100%> (ø)	⬆️
... and 9 more