Add benchmarks

[eligrey]

We should benchmark the time it takes to decrypt and download encrypted files. We still need to decide on a benchmarking framework.

[michaelfarrell76]

Another one that would be useful is max file size? maybe adding a large file in the demo. comparing time unencrypted vs encrypted?

[michaelfarrell76]

customer process x number of files in whatever time, maybe map back to

[michaelfarrell76]

from @eligrey

Raw sequential encrypt/decrypt speed for one probably

[eligrey]

We can implement a useful benchmark by passing large synthetic constant-size ReadableStreams to Penumbra and recording the time that it takes to finish encrypting/decrypting the stream.