Create a single tmp dir per test session

[delucchi-cmu]

Previous behavior was to create a new tmp directory for each test case that required writing to the cloud bucket. That adds a lot of overhead, as removing the directory is a slow, asynchronous call. We have an exponential backoff and retry to delete, but there were around 600 temp directories that were not cleaned up due to failed attempts.

This change creates a single temp directory in the cloud bucket for the whole execution, and cleans it up at the end of the testing session. I increase the number of retries, to get one more chance to successfully delete before giving up.

Because we only have ONE exponential backoff/retry cycle for the whole test session, we trim about 15-30 seconds off the total execution time

In addition, since this changed so many test files, I figured it was an ok time to rename the overly-long example_cloud_storage_options fixture. Also cleans up the session-level fixtures.

[github-actions]

Before [153c401]	After [189db0b]	Ratio	Benchmark (Parameter)
2.66±0.9s	881±1000ms	~0.33	benchmarks.time_computation
2.06k	3.52k	1.71	benchmarks.mem_list

Click here to view all benchmarks.

[jeremykubica]

Looks like a nice change in terms of efficiency. I left two questions for my own understanding.