workload: rewrite workload tool

This patch rewrites the `bank` workload into a more general `workload`
tool, and adds simple `read` and `write` workloads too. It also makes
several opportunistic simplifications of client code.

Cargo.toml

@@ -10,17 +10,20 @@ default-run = "toydb"
 doctest = false
 
 [dependencies]
+async-channel = "~2.2.0"
 bincode = "~1.3.3"
-clap = { version = "~4.5.4", features = ["cargo"] }
+clap = { version = "~4.5.4", features = ["cargo", "derive"] }
 config = "~0.14.0"
 derivative = "~2.2.0"
 fs4 = "~0.8.1"
 futures = "~0.3.15"
 futures-util = "~0.3.15"
+hdrhistogram = "~7.5.4"
 hex = "~0.4.3"
+itertools = "0.12.1"
 lazy_static = "~1.4.0"
 log = "~0.4.14"
-names = "~0.14.0"
+petname = "1.1.3"
 rand = "~0.8.3"
 regex = "1.5.4"
 rustyline = "~14.0.0"