refactor(streaming): remove RwResult in streaming hash join

[yuhao-su]

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What's changed and what's your intention?

as title

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)

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #3476 (f451fcd) into main (62750cd) will increase coverage by 0.01%.
The diff coverage is 87.82%.

@@            Coverage Diff             @@
##             main    #3476      +/-   ##
==========================================
+ Coverage   74.43%   74.44%   +0.01%     
==========================================
  Files         771      771              
  Lines      108446   108464      +18     
==========================================
+ Hits        80718    80746      +28     
+ Misses      27728    27718      -10     

Flag	Coverage Δ
rust	74.44% <87.82%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
src/stream/src/executor/error.rs	5.88% <ø> (+0.24%)	⬆️
src/stream/src/executor/hash_join.rs	96.85% <81.15%> (+0.02%)	⬆️
src/stream/src/executor/managed_state/join/mod.rs	92.92% <94.44%> (+1.60%)	⬆️
src/common/src/hash/key.rs	84.95% <100.00%> (+0.08%)	⬆️
src/stream/src/common/builder.rs	98.96% <100.00%> (+0.04%)	⬆️
src/stream/src/executor/hash_agg.rs	97.82% <100.00%> (-0.01%)	⬇️
src/connector/src/filesystem/file_common.rs	80.35% <0.00%> (-0.45%)	⬇️
src/storage/src/hummock/local_version_manager.rs	79.27% <0.00%> (+0.12%)	⬆️
... and 3 more

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[chinawch007]

Excuse me, what's the meaning of 'degree' in managed_state/join/mod.rs?