Rust

Minor: Document `ExecutionPlan::equivalence_properties` more thoroughly #20119

Job	Run time
cargo check	3m 7s
build with wasm-pack	2m 53s
Check cargo fmt	41s
cargo test (mac)	22m 23s
Verify MSRV	7m 2s
Verify Vendored Code	1m 21s
cargo test (win64)	24m 42s
cargo test doc (amd64)	18m 19s
cargo examples (amd64)	8m 41s
cargo test datafusion-cli (amd64)	5m 33s
cargo test (amd64)	8m 40s
check Cargo.toml formatting	1m 18s
clippy	6m 29s
check configs.md is up-to-date	4m 21s
cargo test hash collisions (amd64)	18m 22s
cargo doc	5m 8s
Run sqllogictest with Postgres runner	2m 55s
cargo test pyarrow (amd64)	2m 1s
verify benchmark results (amd64)	9m 21s
	2h 33m 17s

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