Caching and Watch Mode

Declare the files a task reads with sources (globs). The task is skipped when sources, code, arguments and environment are unchanged since its last successful run. With outputs, it also runs if an output is missing.

## build

```meta
sources = ["src/**/*.rs", "Cargo.toml"]
outputs = ["target/release/app"]
```

```bash
cargo build --release
```

Fingerprints live in .mq-task/cache.json in the invocation directory. Consider git-ignoring .mq-task/. --no-cache ignores them.

Watch

mq-task test --watch

Re-runs whenever any sources of the task or its dependencies, or the task file, change.