update Python support

[LOCEANlloydizard]

update echoshader to support Python 3.13-3.14, aligning with the current echopype Python support. This updates the package metadata, CI, PyPI and ReadTheDocs workflows, and modernizes the installation/development instructions!

Also:

• fixes pre-commit failures caused by the updated Ruff checks
• centralizes documentation dependencies in pyproject.toml and updates ReadTheDocs to install the docs extra

Closes #251
Ref #272

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.89%. Comparing base (c9d4bd9) to head (18d31e3).
⚠️ Report is 57 commits behind head on main.

Files with missing lines	Patch %	Lines
echoshader/echogram.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
+ Coverage   69.27%   69.89%   +0.62%     
==========================================
  Files          11       10       -1     
  Lines         690      691       +1     
==========================================
+ Hits          478      483       +5     
+ Misses        212      208       -4     

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