Reduce network overhead of _refresh_cache

[pjbull]

We used to do a lot of network calls in _refresh_cache, which slowed down scripts that looked at lots of files. This change makes it so _refresh_cache only needs one network call.

• Add a NoStat exception if we can't get stats for a particular path (two cases: could be directory or could not exist)
• Get stats once at top of call

Downsides:

• We used to be able to provide a specific error if somehow you tried to cache a directory instead of a file. I don't think this will happen, so it probably is not worth the additional network call.

On a slow connection, it seems ~4x faster after removing the additional calls. (First _refresh_cache is slow because it actually downloads the file on my slow connection)

BEFORE:

AFTER:

Closes #110

[github-actions]

🚀 Deployed on https://deploy-preview-111--gallant-agnesi-5f7bb3.netlify.app

[codecov]

Codecov Report

Merging #111 (3a3d69b) into master (8b230c3) will decrease coverage by 0.1%.
The diff coverage is 91.4%.

@@           Coverage Diff            @@
##           master    #111     +/-   ##
========================================
- Coverage    91.4%   91.3%   -0.2%     
========================================
  Files           8       8             
  Lines         680     691     +11     
========================================
+ Hits          622     631      +9     
- Misses         58      60      +2     

Impacted Files	Coverage Δ
cloudpathlib/azure/azblobpath.py	92.4% <77.7%> (-3.2%)	⬇️
cloudpathlib/s3/s3client.py	91.6% <85.7%> (-1.7%)	⬇️
cloudpathlib/cloudpath.py	90.1% <100.0%> (+0.4%)	⬆️
cloudpathlib/s3/s3path.py	97.8% <100.0%> (+0.1%)	⬆️

[jayqi]

This looks like a reasonable solution to me.

[pjbull]

Two updates, and I think this is ready to go if all the tests pass.

(1) In testing, found that _upload_local_to_cloud also had repeated stat calls, so refactored that.

(2) While looking for speed improvements, found that filtering the objects list made both our _exists and _is_file_or_dir calls on the S3 client faster. Here are some test runs:

[jayqi]

LGTM! 🎉