perf(store): Add benchmarks

[john-z-yang]

Adds a benchmark for simulating worker ⇔ store interactions.

Use make bench or cargo bench to run.

bench_InflightActivationStore/process_activations
                        time:   [13.091 s 13.313 s 13.525 s]
                        thrpt:  [739.39  elem/s 751.15  elem/s 763.88  elem/s]
                 change:
                        time:   [-21.574% -19.199% -16.927%] (p = 0.00 < 0.05)
                        thrpt:  [+20.376% +23.760% +27.508%]
                        Performance has improved.

[markstory]

Why do you want to sleep in a benchmark test?

[john-z-yang]

I tried letting it run without a sleep, that gives me this error when I have a large number of workers (>16)

'tokio-runtime-worker' panicked at benches/inflight_activation_store_bench.rs:32:18:
called `Result::unwrap()` on an `Err` value: error returned from database: (code: 5) database is locked

Caused by:
    (code: 5) database is locked
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This seems like a very strange error to me as I expect if the db is contended, the .await call would just wait.

Some cursory googling suggests that this is because sqlite is actually single threaded under the hood for writes, and for those 2 calls we're doing writes with UPDATE.

The way I can get around with this error is to force only a single connection when we initialize the pool by pinning the max connection to 1 when the store is being initialized. Or just use a single worker.

let sqlite_pool = PoolOptions::new().max_connections(1).connect(url).await?;

But I feel like that should be a separate change.