refactor(plan_node): simplify insert nodes (probably the last crusade)

[ice1000]

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What's changed and what's your intention?

Follow up of #8898, #8870, #8905, #8930, #8932, #9011, #9044, #9176, #9715, #9740, #9785, #10198.

This is also useful in the series of #10157

Checklist For Contributors

• Yes

Documentation

• My PR DOES NOT contain user-facing changes.

[st1page]

LGTM

[codecov]

Codecov Report

Merging #10232 (7497530) into main (6b4b4e6) will decrease coverage by 0.02%.
The diff coverage is 60.62%.

@@            Coverage Diff             @@
##             main   #10232      +/-   ##
==========================================
- Coverage   70.74%   70.72%   -0.02%     
==========================================
  Files        1236     1237       +1     
  Lines      211701   211710       +9     
==========================================
- Hits       149771   149742      -29     
- Misses      61930    61968      +38     

Flag	Coverage Δ
rust	70.72% <60.62%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...rc/frontend/src/optimizer/plan_node/generic/mod.rs	0.00% <ø> (ø)
src/frontend/src/scheduler/plan_fragmenter.rs	67.57% <0.00%> (ø)
...c/frontend/src/optimizer/plan_node/batch_insert.rs	50.00% <40.00%> (+0.81%)	⬆️
...frontend/src/optimizer/plan_node/generic/delete.rs	80.00% <50.00%> (ø)
...frontend/src/optimizer/plan_node/generic/insert.rs	61.17% <61.17%> (ø)
...frontend/src/optimizer/plan_node/logical_insert.rs	61.76% <72.72%> (-23.07%)	⬇️
src/frontend/src/planner/insert.rs	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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