refactor(datagen): improve datagen connector readability

[ryanrussell]

Signed-off-by: Ryan Russell git@ryanrussell.org

I hereby agree to the terms of the Singularity Data, Inc. Contributor License Agreement.

What's changed and what's your intention?

Improve the datagen connector readability.

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

[codecov]

Codecov Report

Merging #3464 (e184211) into main (c0e02d7) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3464      +/-   ##
==========================================
- Coverage   74.31%   74.31%   -0.01%     
==========================================
  Files         769      769              
  Lines      106773   106773              
==========================================
- Hits        79349    79348       -1     
- Misses      27424    27425       +1     

Flag	Coverage Δ
rust	74.31% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
src/connector/src/datagen/mod.rs	100.00% <ø> (ø)
src/connector/src/datagen/source/generator.rs	98.21% <100.00%> (ø)
src/meta/src/hummock/mock_hummock_meta_client.rs	40.56% <0.00%> (-0.95%)	⬇️
src/frontend/src/expr/utils.rs	98.99% <0.00%> (-0.26%)	⬇️
src/common/src/types/ordered_float.rs	24.70% <0.00%> (-0.20%)	⬇️
src/storage/src/hummock/local_version_manager.rs	84.37% <0.00%> (-0.16%)	⬇️
src/meta/src/rpc/server.rs	80.41% <0.00%> (+0.46%)	⬆️
src/meta/src/manager/id.rs	96.06% <0.00%> (+0.56%)	⬆️

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