Generate GroupByHash output in multiple RecordBatches #72

Job	Run time
cargo test (win64)	41m 53s
cargo check	8m 3s
build with wasm-pack	2m 12s
cargo test (macos)	9m 1s
Check cargo fmt	50s
cargo test (macos-aarch64)	11m 6s
Verify MSRV (Min Supported Rust Version)	6m 12s
Verify Vendored Code	56s
cargo test hash collisions (amd64)	13m 42s
clippy	5m 22s
check configs.md is up-to-date	2m 59s
check Cargo.toml formatting	3m 9s
cargo doc	3m 56s
cargo test (amd64)	9m 31s
cargo test datafusion-cli (amd64)	3m 38s
cargo test doc (amd64)	14m 21s
cargo examples (amd64)	12m 52s
Run sqllogictest with Postgres runner	3m 20s
cargo test pyarrow (amd64)	3m 2s
verify benchmark results (amd64)	11m 15s
	2h 47m 20s

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