fix(rust): Make json readers ignore BOM character

[deanm0000]

Fixes #15301

[codecov]

Codecov Report

Attention: Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.20%. Comparing base (8d43ba1) to head (3dfea6f).
Report is 6 commits behind head on main.

Files	Patch %	Lines
crates/polars-io/src/json/mod.rs	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18240      +/-   ##
==========================================
- Coverage   80.21%   80.20%   -0.02%     
==========================================
  Files        1501     1501              
  Lines      198925   198935      +10     
  Branches     2837     2837              
==========================================
- Hits       159576   159562      -14     
- Misses      38821    38845      +24     
  Partials      528      528              

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[codspeed-hq]

CodSpeed Performance Report

Merging #18240 will not alter performance

_{Comparing deanm0000:json_ignore_bom (3dfea6f) with main (8d43ba1)}

Summary

✅ 37 untouched benchmarks

[ritchie46]

Thanks @deanm0000