perf: Reduce arrow slice mmap overhead

[orlp]

The owner-based arrow array backing is rather slow to create, we already have a static slice storage backing in SharedStorage we can use.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 10 lines in your changes missing coverage. Please review.

Project coverage is 79.28%. Comparing base (e89987d) to head (b93f149).
Report is 26 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-arrow/src/ffi/mmap.rs	33.33%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21113      +/-   ##
==========================================
+ Coverage   79.21%   79.28%   +0.07%     
==========================================
  Files        1589     1589              
  Lines      226497   226509      +12     
  Branches     2594     2594              
==========================================
+ Hits       179420   179598     +178     
+ Misses      46481    46315     -166     
  Partials      596      596              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.