Refactor into cargo-project

Rather than have this logic in the aiken binary, this provides a generic
mechanism to do "something" on file change events.  KtorZ is going to
handle wiring it up to the CLI in the best way for the project.

I tried to write some tests for this, but it's hard to isolate the
watcher logic without wrestling with the borrow checker, or overly
neutering this utility.

crates/aiken-project/Cargo.toml

@@ -26,6 +26,7 @@ indexmap = "1.9.2"
 itertools = "0.10.5"
 miette = { version = "5.9.0", features = ["fancy"] }
 minicbor = "0.19.1"
+notify = "6.1.1"
 owo-colors = { version = "3.5.0", features = ["supports-colors"] }
 pallas = "0.18.0"
 pallas-traverse = "0.18.0"