feat: skip filling NULL for put and delete requests

[waynexia]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

As the title. Test result:

• Cut put latency by half

• Double put throughput (18w to 42w)

Before	After

• No regression in TSBS (and somehow has a little improvement...)

Before

Summary:
loaded 1036800000 metrics in 190.468sec with 6 workers (mean rate 5443439.71 metrics/sec)
loaded 103680000 rows in 190.468sec with 6 workers (mean rate 544343.97 rows/sec)

After

Summary:
loaded 1036800000 metrics in 187.196sec with 6 workers (mean rate 5538568.26 metrics/sec)
loaded 103680000 rows in 187.196sec with 6 workers (mean rate 553856.83 rows/sec)

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.

Refer to a related PR or issue link (optional)

[fengjiachun]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1dc4fec) 85.43% compared to head (855847c) 84.98%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3364      +/-   ##
==========================================
- Coverage   85.43%   84.98%   -0.46%     
==========================================
  Files         889      889              
  Lines      145471   145458      -13     
==========================================
- Hits       124288   123621     -667     
- Misses      21183    21837     +654     

[tisonkun]

Nice catch!