feat: lazy initialize vector builder on write

[waynexia]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Lazy create MutableVector for TimeSeries. This change can save lots of memory when the data's field columns are sparse. In my test scenario where ~90% fields are null, it can cut up to 80% memory consumption:

I also run a tsbs-load benchmark to see if this change slow down the normal case. The result shows it doesn't have bad influence:

before this change:

loaded 86400000 rows in 141.686sec with 6 workers (mean rate 609798.27 rows/sec)

after this change:

loaded 86400000 rows in 140.448sec with 6 workers (mean rate 615174.51 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)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6320590) 85.81% compared to head (0c2b2e8) 85.37%.
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3210      +/-   ##
==========================================
- Coverage   85.81%   85.37%   -0.44%     
==========================================
  Files         832      840       +8     
  Lines      136308   137598    +1290     
==========================================
+ Hits       116967   117479     +512     
- Misses      19341    20119     +778     

[v0y4g3r]

LGTM