Useful in tooling, releases, etc - where Dart is available
Example usages:
```bash
# Monorepo world
❯ dart ./dev/tools/bin/engine_hash.dart -s head
226e13826c7253c968d798666f323b1f207979f8
# Non-monorepo world
❯ dart ./dev/tools/bin/engine_hash.dart -s head
Error calculating engine hash: Not in a monorepo
```
