Use moto-server to create a local S3 service.

[delucchi-cmu]

Creates a new test mode, local_s3, which spins up a local s3 instance, using moto_server. This operates like a pretty real s3 instance, and drops all of its data after termination.

Adds a directory of files that are copied onto the s3 instance when it spins up.

Note that s3 has some quirks around directories not being real. We also add some logic that incorporates this in expectations.

[github-actions]

Before [f3cdc02]	After [cc97abb]	Ratio	Benchmark (Parameter)
3.63±1s	3.10±0.9s	~0.85	benchmarks.time_computation
1.05k	3.99k	3.81	benchmarks.mem_list

Click here to view all benchmarks.

[hombit]

Looks great, thank you!