refactor(rust): Improve hash join build sample implementation

[orlp]

Small things like not holding on to memory, respecting stop requests, not letting multiple values in single pipeline, etc, and cleaned up code.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 208 lines in your changes missing coverage. Please review.

Project coverage is 79.86%. Comparing base (9bcff72) to head (62d5534).
Report is 34 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-stream/src/nodes/joins/equi_join.rs	0.00%	208 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21236      +/-   ##
==========================================
+ Coverage   79.75%   79.86%   +0.10%     
==========================================
  Files        1593     1596       +3     
  Lines      228119   228463     +344     
  Branches     2600     2607       +7     
==========================================
+ Hits       181947   182455     +508     
+ Misses      45575    45412     -163     
+ Partials      597      596       -1     

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