Document useful module-level constants

[anshurajbisoyi98-ctrl]

• Closes Document internal module-level constants #2096
• I am familiar with the contributing guidelines
• I attest that all AI-generated material has been vetted for accuracy and is in compliance with the pvlib license
• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

This change documents useful module-level constants on existing API reference pages near the functions and models they support. The albedo tables appear with irradiance references, the airmass model collections and Hellmann exponents with atmospheric references, and temperature model parameters with temperature models. The constants retain concise module-level docstrings.

Validation

• make -C docs/sphinx html: passed; build succeeded (one Sphinx cache warning about html_context). Checked the rendered airmass_atmospheric, irradiance/other, and pv_modeling/temperature pages; all requested constants are present and no broken-reference warning occurred.
• pytest -q tests/test_albedo.py tests/test_atmosphere.py tests/test_temperature.py: passed, 64 tests.
• git diff --check: passed.

[kandersolar]

@anshurajbisoyi98-ctrl this PR creates a new page to group unrelated constants together, which is not what was discussed in the issue:

they should be documented near where they belong

documenting the variables near the functions they are related to

Instead of putting all the constants on one page, please put them in existing pages near relevant functions.

[anshurajbisoyi98-ctrl]

Moved the constants to the existing pages near related functions and removed the constants page. Docs build checked.

[cwhanse]

@anshurajbisoyi98-ctrl thanks for having the AI show how the constants could be documented. We don't have time to fix the placement and text of the constant docstrings in this PR.