fix(rust): Add ScanSources in prelude

[AntoinePrv]

polars_plan::plan::ScanSources should be part of polars_lazy::prelude because it is a parameter of polars_lazy::prelude::LazyCsvReader::new_with_sources.

AFAIK the only way to use it now ina third party project is to add a direct dependency on polars_plan.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.00%. Comparing base (2ae01fb) to head (ac9de5a).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20420      +/-   ##
==========================================
+ Coverage   78.98%   79.00%   +0.01%     
==========================================
  Files        1562     1562              
  Lines      220103   220166      +63     
  Branches     2486     2486              
==========================================
+ Hits       173855   173945      +90     
+ Misses      45675    45648      -27     
  Partials      573      573              

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