Bugfix for python v3.10 and add bolometer observer test

[munechika-koyo]

Key changes include:

• Fix inavailable type setting for python v3.10 (using Self type)

• Added built-in dataset functionality for bolometer mock data.

• Updated visualization to display the percentage of rays passed.

• Refactored documentation for clarity and consistency.

• Introduced tests for loading and visualizing bolometer data.

[Copilot]

Pull request overview

This PR improves bolometer observer usability and documentation by introducing a built-in mock bolometer IMAS dataset, adding observer-focused docs/tests, and adjusting visualization output, while also fixing Python 3.10 typing compatibility in bolometer enums.

Changes:

• Replace Self-based enum return annotations with forward-referenced concrete enum types for Python 3.10 compatibility.
• Add a built-in mock bolometer dataset generator (datasets.bolometer_moc) and use it in new observer tests and a new documentation notebook.
• Update bolometer visualization titles to display the ray-through ratio as a percentage; reorganize docs gallery and notebook metadata formatting.

Reviewed changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
tests/observer/test_bolometer.py	Adds smoke tests for loading and visualizing bolometer observers.
tests/observer/conftest.py	Adds a session fixture providing a temp-path bolometer dataset.
src/cherab/imas/observer/bolometer.py	Updates visualization title to report ray pass rate as a percentage.
src/cherab/imas/observer/init.py	Exposes bolometer module via __all__.
src/cherab/imas/ids/bolometer/utility.py	Fixes typing annotations for Python 3.10 compatibility in enum helpers.
src/cherab/imas/datasets/_fetchers.py	Refines dataset path examples in docstrings.
src/cherab/imas/datasets/_builtin.py	Introduces built-in mock bolometer dataset generation and caching.
src/cherab/imas/datasets/init.py	Exports the new built-in dataset helper and updates module docs.
docs/source/examples.md	Adds an “Observer” notebook gallery section.
docs/source/conf.py	Adds an nbsphinx thumbnail for the bolometer notebook.
docs/notebooks/plasma/emission.ipynb	Normalizes raw-cell metadata formatting.
docs/notebooks/observer/bolometer.ipynb	Adds a new bolometer observer usage/visualization notebook.
docs/notebooks/misc/fractional_abundances.ipynb	Normalizes raw-cell metadata and improves inline reference markup.
CHANGELOG.md	Documents additions/changes/fixes for release 0.4.1.

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[codecov]

Codecov Report

❌ Patch coverage is 95.26627% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.10%. Comparing base (052948f) to head (70fc172).
⚠️ Report is 22 commits behind head on master.

Files with missing lines	Patch %	Lines
src/cherab/imas/datasets/_builtin.py	96.83%	3 Missing and 2 partials ⚠️
src/cherab/imas/ids/bolometer/utility.py	50.00%	2 Missing ⚠️
src/cherab/imas/observer/bolometer.py	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #29       +/-   ##
===========================================
+ Coverage   50.41%   64.10%   +13.69%     
===========================================
  Files          45       46        +1     
  Lines        2650     2811      +161     
  Branches      453      468       +15     
===========================================
+ Hits         1336     1802      +466     
+ Misses       1137      804      -333     
- Partials      177      205       +28     

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