refactor(query): split internals into submodules and slim down query.rs (#6)

Author: beinan

rust/lance-graph/CONTRIBUTING.md

@@ -0,0 +1,14 @@
+Contributing (Rust crate)
+=========================
+
+Before pushing or opening a PR, please verify Rust code formatting matches CI:
+
+```bash
+cargo fmt --manifest-path rust/lance-graph/Cargo.toml -- --check
+```
+
+If the check fails, format the code locally:
+
+```bash
+cargo fmt --manifest-path rust/lance-graph/Cargo.toml
+```