refactor(rust): Add equi joins to new streaming engine

[orlp]

Still a work in progress, do not merge.

[codecov]

Codecov Report

Attention: Patch coverage is 0.46904% with 1061 lines in your changes missing coverage. Please review.

Project coverage is 79.10%. Comparing base (426cf27) to head (a83f38e).
Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-stream/src/nodes/joins/equi_join.rs	0.00%	649 Missing ⚠️
...s/polars-expr/src/chunked_idx_table/row_encoded.rs	0.00%	232 Missing ⚠️
crates/polars-expr/src/hash_keys.rs	0.00%	123 Missing ⚠️
crates/polars-utils/src/idx_map/bytes_idx_map.rs	0.00%	14 Missing ⚠️
crates/polars-core/src/frame/mod.rs	30.00%	7 Missing ⚠️
crates/polars-utils/src/index.rs	25.00%	6 Missing ⚠️
crates/polars-core/src/datatypes/field.rs	0.00%	4 Missing ⚠️
crates/polars-ops/src/frame/join/args.rs	0.00%	4 Missing ⚠️
crates/polars-stream/src/nodes/in_memory_map.rs	0.00%	4 Missing ⚠️
crates/polars-stream/src/nodes/in_memory_source.rs	0.00%	4 Missing ⚠️
... and 5 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19869      +/-   ##
==========================================
- Coverage   79.43%   79.10%   -0.33%     
==========================================
  Files        1551     1559       +8     
  Lines      215222   217441    +2219     
  Branches     2452     2456       +4     
==========================================
+ Hits       170954   172014    +1060     
- Misses      43710    44869    +1159     
  Partials      558      558              

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