Avoid replication of x

[mayer79]

This PR brings some code changes:

• The masker now does not require replicated x anymore, requiring significantly less memory and bringing some speed-up for data.frames.
• Matrix input can now also be modified by feature_names.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.83%. Comparing base (04df689) to head (d128feb).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
+ Coverage   96.73%   96.83%   +0.10%     
==========================================
  Files           7        7              
  Lines         674      664      -10     
==========================================
- Hits          652      643       -9     
+ Misses         22       21       -1     

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