feat: Defines more structs and methods for a partitioned merge tree #13511

Job	Run time
Check (windows-latest)	5m 37s
Clippy	2m 14s
Build GreptimeDB binaries (ubuntu-20.04)	4m 23s
Check (ubuntu-20.04)	1m 36s
coverage	10m 18s
Rustfmt	20s
Toml Check	23s
Spell Check with Typos	15s
Compatibility Test	29s
Sqlness Test (ubuntu-20.04)	1m 53s
Sqlness Test with Kafka Wal (ubuntu-20.04)	2m 33s
	30m 1s

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