fix readthedocs build

[orbeckst]

Fixes #99 and #75

Changes made in this Pull Request:

• RTD config update
  • use os = ubuntu-lts-latest
  • use tools.python = "miniforge3-latest"
• bump sphinx to >= 7.2.0
  • required for making it work under Python 3.14 (otherwise error due ast.Str missing)
  • removed pin on myst-parser (required for sphinx>=7)
• fixed the pydantic example (would not pass with pydantic > 1)

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

[orbeckst]

New errors:

/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/docutils/utils/math/latex2mathml.py:954: SyntaxWarning: "\i" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\i"? A raw string is also an option.
  node = parse_latex_math(node, '\int\dotsi\int')
Running Sphinx v6.2.1
making output directory... done
[autosummary] generating autosummary for: additional_samples.rst, autodoc_pydantic_example.rst, change-log.rst, customization.rst, index.rst, license.rst, mdanalysis.rst, notebook.ipynb, numpydoc_example.rst, primer.rst, pymethod.rst, rst-cheatsheet/rst-cheatsheet.rst, specimen.rst, subpage/index.rst, subpage/second-subsubpage.rst, subpage/subsubpage.rst, writing-references.rst
Matplotlib is building the font cache; this may take a moment.
Failed to import pydantic_example.
Possible hints:
* KeyError: 'pydantic_example'
* PydanticImportError: `BaseSettings` has been moved to the `pydantic-settings` package. See https://docs.pydantic.dev/2.13/migration/#basesettings-has-moved-to-pydantic-settings for more details.

[orbeckst]

Additional (?) error:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/__init__.py", line 125, in analyze
    parser.parse()
    ~~~~~~~~~~~~^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 554, in parse
    self.parse_comments()
    ~~~~~~~~~~~~~~~~~~~^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 561, in parse_comments
    picker.visit(tree)
    ~~~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 321, in visit
    super().visit(node)
    ~~~~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/ast.py", line 506, in visit
    return visitor(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/ast.py", line 514, in generic_visit
    self.visit(item)
    ~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 321, in visit
    super().visit(node)
    ~~~~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/ast.py", line 506, in visit
    return visitor(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 437, in visit_ClassDef
    self.visit(child)
    ~~~~~~~~~~^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 321, in visit
    super().visit(node)
    ~~~~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/ast.py", line 506, in visit
    return visitor(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 452, in visit_FunctionDef
    self.visit(child)
    ~~~~~~~~~~^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 321, in visit
    super().visit(node)
    ~~~~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/ast.py", line 506, in visit
    return visitor(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/ast.py", line 514, in generic_visit
    self.visit(item)
    ~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 321, in visit
    super().visit(node)
    ~~~~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/ast.py", line 506, in visit
    return visitor(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 426, in visit_Try
    self.visit(subnode)
    ~~~~~~~~~~^^^^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 321, in visit
    super().visit(node)
    ~~~~~~~~~~~~~^^^^^^
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/ast.py", line 506, in visit
    return visitor(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/parser.py", line 403, in visit_Expr
    isinstance(node.value, ast.Str)):
                           ^^^^^^^
AttributeError: module 'ast' has no attribute 'Str'

...


Exception occurred:
  File "/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/sphinx/pycode/__init__.py", line 141, in analyze
    raise PycodeError(f'parsing {self.srcname!r} failed: {exc!r}') from exc
sphinx.errors.PycodeError: parsing '/home/docs/checkouts/readthedocs.org/user_builds/mdanalysis-sphinx-theme/conda/100/lib/python3.14/site-packages/MDAnalysis/core/topologyattrs.py' failed: AttributeError("module 'ast' has no attribute 'Str'")

[orbeckst]

@lilyminium are you happy with this upgrade?