refactor: Refactor code for re-use by streaming NDJSON source

[nameexhaustion]

Some moving / factoring of functions for the NDJSON source

• Moves some memory prefetch functions from io_sources/parquet under new streaming to polars-utils

[nameexhaustion]

The code in this section isn't changed - I'm not sure why there's a big diff

on local -

[codecov]

Codecov Report

Attention: Patch coverage is 58.01887% with 89 lines in your changes missing coverage. Please review.

Project coverage is 79.81%. Comparing base (69612d4) to head (317b7b1).
Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-utils/src/mem.rs	49.15%	60 Missing ⚠️
crates/polars-io/src/ndjson/core.rs	61.53%	15 Missing ⚠️
...c/nodes/io_sources/parquet/row_group_data_fetch.rs	64.86%	13 Missing ⚠️
crates/polars-io/src/ndjson/mod.rs	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21520      +/-   ##
==========================================
- Coverage   79.81%   79.81%   -0.01%     
==========================================
  Files        1592     1591       -1     
  Lines      229268   229310      +42     
  Branches     2623     2623              
==========================================
+ Hits       182987   183016      +29     
- Misses      45676    45689      +13     
  Partials      605      605              

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