Update contributing guidelines

[jeandet]

This pull request updates the project's contribution guidelines and testing configuration to modernize the development process, clarify expectations for contributors, and align with current Python versions. The most important changes are summarized below:

Documentation and Contribution Guidelines Updates:

• Updated all references from "Space Physics WebServices Client" and SPEASY to "Speasy" for consistency and clarity throughout CONTRIBUTING.rst. [1] [2]
• Expanded the documentation on setting up the development environment, recommending the use of Python virtual environments and providing clearer installation instructions for dependencies and development requirements.
• Added a new section with coding guidelines, including adherence to PEP 8, use of numpy docstring style, writing tests for new functionality, and guidance on extending the core modules and adding providers or codecs.

Testing and Python Version Support:

• Updated the list of supported Python versions to 3.10–3.14 (removing 3.6–3.9) in both the contribution guidelines and tox.ini, and added Python 3.14 to the test matrix. [1] [2]
• Improved instructions for running tests and documentation checks, including how to run all tests, quick tests, and documentation tests, with updated make commands.

Bug Fixing and Best Practices:

• Added a reminder for contributors fixing bugs to include a test that reproduces the bug and reference the relevant issue in the non-regression test.

[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 SonarQube Cloud