Rust

Refactor TreeNode and cleanup some implementations #600

Job	Run time
cargo check	6m 39s
build with wasm-pack	1m 56s
Check cargo fmt	37s
cargo test (mac)	11m 56s
Verify Vendored Code	48s
cargo test (win64)	3h 22m 9s
Verify MSRV	6m 18s
cargo test doc (amd64)	9m 24s
cargo doc	3m 2s
check Cargo.toml formatting	1m 17s
check configs.md is up-to-date	2m 11s
cargo test hash collisions (amd64)	8m 38s
clippy	2m 7s
cargo test datafusion-cli (amd64)	2m 49s
cargo examples (amd64)	6m 26s
Run sqllogictest with Postgres runner	3m 2s
cargo test pyarrow (amd64)	2m 7s
verify benchmark results (amd64)	9m 35s
cargo test (amd64)	9m 8s
	4h 50m 9s

Provide feedback