Adds codec interface + registry and migrate existing code

[jeandet]

This pull request includes various updates primarily focused on enhancing the configuration, updating Python version support, and refactoring the codebase for better modularity and maintainability. The most important changes include updating Python versions in the CI workflows, adding a new codec interface, and refactoring the CDF handling code.
It also drops support for AMDA CSV format.

Configuration Updates:

• .editorconfig: Added max_line_length = 120 to enforce a maximum line length.

CI Workflow Updates:

• .github/workflows/PRs.yml: Updated the supported Python versions to include 3.9 to 3.13 and removed 3.8. [1] [2]
• .github/workflows/tests.yml: Updated the supported Python versions to include 3.9 to 3.13 and removed 3.8. [1] [2]
• .github/workflows/pythonpublish.yml: Updated the Python version from 3.8 to 3.9.

Code Refactoring:

• speasy/core/cdf/__init__.py: Removed the entire file which contained various helper functions and classes for handling CDF files.
• speasy/core/codecs/__init__.py: Added imports for CodecInterface, register_codec, get_codec, and user_codecs_dir and included bundled codecs.
• speasy/core/codecs/codec_interface.py: Introduced a new CodecInterface class to define the protocol for codecs.
• speasy/core/codecs/bundled_codecs/istp_cdf.py: Added a new codec class IstpCdf for handling ISTP CDF files, including methods for loading and saving variables.

Minor Code Changes:

• speasy/config/__init__.py: Added a new configuration entry user_codecs_extra_dirs and updated the description for output_format. [1] [2]
• speasy/core/any_files.py: Changed how headers are accessed in _cached_get_remote_file function.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 71.76471% with 24 lines in your changes missing coverage. Please review.

Project coverage is 86.56%. Comparing base (771819c) to head (40dfac9).
Report is 38 commits behind head on main.

Files with missing lines	Patch %	Lines
speasy/core/codecs/codecs_registry.py	66.66%	8 Missing and 5 partials ⚠️
speasy/core/codecs/codec_interface.py	70.00%	6 Missing ⚠️
...ct_archive_downloader/direct_archive_downloader.py	50.00%	1 Missing and 1 partial ⚠️
speasy/webservices/amda/_impl.py	83.33%	1 Missing ⚠️
speasy/webservices/amda/ws.py	50.00%	1 Missing ⚠️
speasy/webservices/csa/__init__.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #154      +/-   ##
==========================================
- Coverage   86.61%   86.56%   -0.05%     
==========================================
  Files          54       57       +3     
  Lines        3548     3499      -49     
  Branches      578      548      -30     
==========================================
- Hits         3073     3029      -44     
+ Misses        308      303       -5     
  Partials      167      167              

Flag	Coverage Δ
unittests	85.79% <71.76%> (-0.82%)	⬇️

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