feat: add record batch mem stats

[jiacai2050]

Rationale

When some metrics contains more than one subtask, it's helpful to collect them together for output.

Detailed Changes

• Update metric macro, add metric operator.

Test Plan

Update basic UT to test this. This is what I get in my test env:

# Before
        scan_sst_6655:                                                                                                                                                                            
            project_record_batch=847.03µs                                                                                                                                                         
            project_record_batch=1.182922ms                                                                                                                                                       
            project_record_batch=1.208636ms                                                                                                                                                       
            project_record_batch=1.246589ms                                                                                                                                                       
            project_record_batch=1.296161ms                                                                                                                                                       
            project_record_batch=1.323357ms                                                                                                                                                       
            project_record_batch=1.4293ms                                                                                                                                                                      

# After
        scan_sst_6655:                                                                                                                                                                            
            project_record_batch=10.170503ms 

[ShiKaiWi]

LGTM