feat: Parse SMI BeGaze raw data files

[saeub]

Description

Read BeGaze text files. Not aiming for full support for now (I don't have enough data for testing), but at least the raw samples and events in DIDEC should be parsed successfully (#980).

Documentation on file format: https://psychologie.unibas.ch/fileadmin/user_upload/psychologie/Forschung/N-Lab/SMI_BeGaze_Manual.pdf#page=343.21

#945 should be merged first (so that events can be implemented and tested the same way as for EyeLink)

Fixes #981

Implemented changes

Insert a description of the changes implemented in the pull request.

• Implement parse_begaze() like parse_eyelink()
• Implement from_begaze() like from_asc()
• ❓ Figure out a way to route BeGaze files through from_begaze() when loading datasets, even if the file extension is .txt (currently they are routed through from_csv(), not sure if this behavior is required by other datasets)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change is or requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.
Provide instructions so we can reproduce.
Please also list any relevant details for your test configuration

• test_parse_begaze()
• Update test_parse_begaze() after feat: parse eyelink events #945 is merged
• DIDEC tests

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

Attention: Patch coverage is 66.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 99.88%. Comparing base (2d9da18) to head (550945b).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pymovements/gaze/_utils/parsing.py	66.66%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main    #1013      +/-   ##
===========================================
- Coverage   100.00%   99.88%   -0.12%     
===========================================
  Files           79       79              
  Lines         3586     3594       +8     
  Branches       632      634       +2     
===========================================
+ Hits          3586     3590       +4     
- Misses           0        2       +2     
- Partials         0        2       +2     

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