contributing: recommend bacon over cargo-watch

As of [1], `cargo-watch` is on minimal development and officially
recommends `bacon` as a successor.

[1]: watchexec/cargo-watch@9f27bc1,

docs/contributing.md

@@ -134,15 +134,13 @@ One-time setup:
 
     rustup toolchain add nightly  # wanted for 'rustfmt'
     rustup toolchain add 1.76     # also specified in Cargo.toml
-    cargo install cargo-insta
-    cargo install cargo-watch
-    cargo install cargo-nextest
+    cargo install --locked bacon
+    cargo install --locked cargo-insta
+    cargo install --locked cargo-nextest
 
 During development (adapt according to your preference):
 
-    cargo watch --ignore '.jj/**' -s \
-      'cargo clippy --workspace --all-targets \
-       && cargo +1.76 check --workspace --all-targets'
+    bacon clippy-all
     cargo +nightly fmt # Occasionally
     cargo nextest run --workspace # Occasionally
     cargo insta test --workspace --test-runner nextest # Occasionally
@@ -178,9 +176,8 @@ These are listed roughly in order of decreasing importance.
 4. Your code needs to pass `cargo clippy`. You can also
    use `cargo +nightly clippy` if you wish to see more warnings.
 
-5. You may also want to install and use `cargo-watch`. In this case, you should
-   exclude `.jj`. directory from the filesystem watcher, as it gets updated on
-   every `jj log`.
+5. You may also want to install and use [`bacon`](https://dystroy.org/bacon/),
+   to automatically build, check, and / or run tests.
 
 6. To run tests more quickly, use `cargo nextest run --workspace`. To
    use `nextest` with `insta`, use `cargo insta test --workspace

flake.nix

@@ -178,10 +178,10 @@
           pkg-config
 
           # Additional tools recommended by contributing.md
+          bacon
           cargo-deny
           cargo-insta
           cargo-nextest
-          cargo-watch
 
           # Miscellaneous tools
           watchman