Add mktestdocs to catch docs/code drift

[cianc]

Description

Adds automated testing of Python code examples in the documentation to prevent examples from drifting out of sync with the library.

• Add mktestdocs and pytest to the doc dependency group in pyproject.toml so they are available alongside the other doc-build tools without pulling in the full dev group.

• Add scripts/check-docs-drift.py: a pytest-based script that uses mktestdocs.grab_code_blocks() to collect every ```python fenced block under docs/, skips any block whose first line is `# skip`, and executes the rest via `exec_python()`. A new taskipy task `docs-check-drift` runs it with `pytest scripts/check-docs-drift.py -v`.

• Fix all ```python code blocks across docs/ so they are correctly picked up by mktestdocs:

  • Remove the stray space in python fences (changed topython) so that mktestdocs can identify them (it matches on the exact string "python" immediately after the backticks).
  • Add save_to_file=False, log_level="error" to EmissionsTracker and OfflineEmissionsTracker instantiations to avoid creating CSV files or noisy output during CI runs.
  • Add # skip as the first line of blocks that cannot run in CI because they depend on external services or optional heavy dependencies (TensorFlow, Prometheus, Logfire, Google Cloud, Comet ML, live CodeCarbon API).
  • Correct a pip install command that was incorrectly fenced as python in `comet.md`; changed to console.

• Update .github/workflows/build-docs.yml to run docs-check-drift as a step before the docs build, triggered on changes to docs/**, mkdocs.yml, or scripts/check-docs-drift.py.

• Document the drift check and the # skip convention in CONTRIBUTING.md under the "Build Documentation" section.

Related Issue

Please link to the issue this PR resolves: #1083

Motivation and Context

Helps prevent drift of code blocks in documentation

How Has This Been Tested?

Ran all tests including new mktestdocs tests.

Screenshots (if appropriate):

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• 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 change)

Checklist:

Go over all the following points, and put an x in all the boxes that apply.

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.22%. Comparing base (9be333a) to head (9057de3).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1096   +/-   ##
=======================================
  Coverage   78.22%   78.22%           
=======================================
  Files          38       38           
  Lines        3632     3632           
=======================================
  Hits         2841     2841           
  Misses        791      791           

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