Add canopydb to the benchmarks

[arthurprs]

Adding Canopydb to the benchmarks. I had this for a while but realized I never opened a PR.

Other additional changes

• Make a lot of values module-level constants
• Use a sync barrier in multi-threaded sections to reduce variance
• Use rng fill functions whenever possible
• Add some basic configuration to Rocksdb. These should be closer to Fjall defaults, for example.
• Instantiate an env_logger instance. This is a noop in practice, but helps development.

[cberner]

canopy looks a bit immature, so I don't want to add it now. Feel free to re-open when it's more widely used and mature.

Those other changes sound reasonable though, if you'd like to send just those, I can review them

[arthurprs]

That's fair. I'll close this one for now and will follow up with a subset in another PR.