feat: group requests by peer

[fengjiachun]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

What's changed and what's your intention?

Minor improve, group the requests by datanode peer, it is good for this case: there are multiple regions of one table on the same datanode

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.

[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 85.11%. Comparing base (f49cd0c) to head (d686782).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3619      +/-   ##
==========================================
- Coverage   85.41%   85.11%   -0.30%     
==========================================
  Files         932      932              
  Lines      155075   155148      +73     
==========================================
- Hits       132451   132056     -395     
- Misses      22624    23092     +468     

[fengys1996]

LGTM