perf: more benchmarks for memtables

[evenyag]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

• Tracking issue for the memtable improvement #2804

What's changed and what's your intention?

This PR adds two new benchmarks for memtables. It simulates data generated by TSBS: 4k hosts and 10s log interval.

• full_scan benches speed to scan all rows and columns in a memtable
• filter_1_host benches speed to scan and filter rows of 1 host
• all benchmarks bench both time_series and the new memtable

It also removes a redundant file bench_merge_tree.rs in the benchmark

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

[v0y4g3r]

LGTM

[fengjiachun]

LGTM