refactor(plan_node): reorganize and simplify source-related nodes

[ice1000]

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What's changed and what's your intention?

Follow up of #8898, #8870, #8905, #8930, #8932, #9011, #9044, #9176.

Checklist For Contributors

• Yes

Documentation

• My PR DOES NOT contain user-facing changes.

[codecov]

Codecov Report

Merging #9209 (7b169b6) into main (59621a6) will decrease coverage by 0.01%.
The diff coverage is 83.92%.

@@            Coverage Diff             @@
##             main    #9209      +/-   ##
==========================================
- Coverage   70.83%   70.82%   -0.01%     
==========================================
  Files        1201     1201              
  Lines      200425   200407      -18     
==========================================
- Hits       141971   141943      -28     
- Misses      58454    58464      +10     

Flag	Coverage Δ
rust	70.82% <83.92%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
src/frontend/src/scheduler/plan_fragmenter.rs	66.71% <0.00%> (ø)
...timizer/plan_visitor/relation_collector_visitor.rs	69.69% <50.00%> (ø)
...frontend/src/optimizer/plan_node/generic/source.rs	93.54% <66.66%> (-6.46%)	⬇️
...c/frontend/src/optimizer/plan_node/batch_source.rs	70.96% <83.33%> (+7.63%)	⬆️
...frontend/src/optimizer/plan_node/logical_source.rs	70.67% <100.00%> (-1.07%)	⬇️
.../frontend/src/optimizer/plan_node/stream_source.rs	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes

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