feat: Add gaze.transforms.smooth()

[jakobchwastek]

Description

Fixes issue #301

Implemented changes

Implementation of transforms.smooth function for smoothing data. The following methods have been
implemented

• Moving Average
• Exponential Moving Average
• Savitzky Golay

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Tested smoothing methods by applying them to a simple 2D array with values [[0., 0.], [1., 1.], [0., 0.]].

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (c8ef04d) 100.00% compared to head (67bbbde) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #555   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           52        52           
  Lines         2258      2289   +31     
  Branches       559       570   +11     
=========================================
+ Hits          2258      2289   +31     

Files	Coverage Δ
src/pymovements/gaze/gaze_dataframe.py	100.00% <100.00%> (ø)
src/pymovements/gaze/transforms.py	100.00% <100.00%> (ø)

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[jakobchwastek]

Adding smooth as transformation method in GazeDataFrame is missing!

[dkrako]

Thanks a lot for this great work!