refactor: make sql function in scripts return a list of column vectors

[killme2008]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

The current sql function in the coprocessor returns a list of lists such as list[list[vector]]. The query result is a list of RecordBatch and it converts eachRecordBatch into a list of column vectors. It's not friendly to users and batch splitting is not necessary at all for the coprocessor.

So in this PR, I changed the return result type to list[Vector]: a list of column vectors. It concatenates all vectors from each batch into one vector for each column.

For example:

import greptime

greptime.query().sql("select number as a, number as b from numbers limit 10")

It will return a list of two elements:

• The first one is a column and which is a vector.
• The second one is b column and which is a vector too.

It's much easier for users to process the query result.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #1243 (06e274b) into develop (6f81717) will decrease coverage by 0.50%.
The diff coverage is 47.50%.

@@             Coverage Diff             @@
##           develop    #1243      +/-   ##
===========================================
- Coverage    85.55%   85.06%   -0.50%     
===========================================
  Files          495      495              
  Lines        72771    72790      +19     
===========================================
- Hits         62261    61917     -344     
- Misses       10510    10873     +363     

[waynexia]

LGTM