refactor(plan_node): Use simple structures

[ice1000]

I hereby agree to the terms of the RisingWave Labs, Inc. Contributor License Agreement.

What's changed and what's your intention?

I have removed the need of some stupid intermediate structures that exist only for historical reasons.

Checklist For Contributors

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• I have demonstrated that backward compatibility is not broken by breaking changes and created issues to track deprecated features to be removed in the future. (Please refer to the issue)
• All checks passed in ./risedev check (or alias, ./risedev c)

Documentation

• My PR DOES NOT contain user-facing changes.

[st1page]

LGTM

need to change the plan node id back

[codecov]

Codecov Report

Merging #8870 (5040a07) into main (1f14219) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #8870      +/-   ##
==========================================
- Coverage   70.81%   70.80%   -0.01%     
==========================================
  Files        1181     1181              
  Lines      195790   195771      -19     
==========================================
- Hits       138644   138613      -31     
- Misses      57146    57158      +12     

Flag	Coverage Δ
rust	70.80% <100.00%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
...rontend/src/optimizer/plan_node/batch_hash_join.rs	91.06% <100.00%> (-0.25%)	⬇️
...c/frontend/src/optimizer/plan_node/generic/join.rs	93.88% <100.00%> (+0.15%)	⬆️
...c/frontend/src/optimizer/plan_node/logical_join.rs	90.22% <100.00%> (-0.05%)	⬇️
...ntend/src/optimizer/plan_node/stream_delta_join.rs	96.38% <100.00%> (-0.11%)	⬇️
...ontend/src/optimizer/plan_node/stream_hash_join.rs	92.03% <100.00%> (+0.17%)	⬆️
...ontend/src/optimizer/rule/index_delta_join_rule.rs	91.91% <100.00%> (+0.08%)	⬆️
src/frontend/src/scheduler/distributed/query.rs	69.15% <100.00%> (-0.43%)	⬇️

... and 5 files with indirect coverage changes

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