chore: split plan.proto and rename projection to project

[TennyZhuang]

What's changed and what's your intention?

PLEASE DO NOT LEAVE THIS EMPTY !!!

1. split "plan.proto" to "plan_common.proto" and "batch_plan.proto"
2. rename batch::projection to batch::project
3. remove some outdated commented codes.
4. add FLUSH in TPC-H e2e test.

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests

Refer to a related PR or issue link (optional)

[fuyufjh]

🐮🍺

[BugenZhao]

L🐮TM

[codecov]

Codecov Report

Merging #2083 (2845b3a) into main (b1d2349) will decrease coverage by 0.00%.
The diff coverage is 55.55%.

@@            Coverage Diff             @@
##             main    #2083      +/-   ##
==========================================
- Coverage   71.06%   71.05%   -0.01%     
==========================================
  Files         635      635              
  Lines       81619    81620       +1     
==========================================
- Hits        58000    57999       -1     
- Misses      23619    23621       +2     

Flag	Coverage Δ
rust	71.05% <55.55%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
src/batch/src/execution/local_exchange.rs	67.03% <ø> (ø)
src/batch/src/executor/create_table.rs	52.54% <ø> (ø)
src/batch/src/executor/drop_stream.rs	0.00% <ø> (ø)
src/batch/src/executor/drop_table.rs	0.00% <ø> (ø)
src/batch/src/executor/generate_series.rs	66.26% <ø> (ø)
src/batch/src/executor/generic_exchange.rs	59.15% <ø> (ø)
src/batch/src/executor/join/hash_join.rs	85.57% <ø> (ø)
src/batch/src/executor/join/mod.rs	63.15% <ø> (ø)
src/batch/src/executor/join/nested_loop_join.rs	82.17% <ø> (ø)
src/batch/src/executor/join/sort_merge_join.rs	74.35% <ø> (ø)
... and 83 more

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