Fix in ModelChain POA methods by adding examples

[Chirag3841]

• Closes Run ModelChain from POA irradiance #943 (documentation portion only)
• I am familiar with the contributing guidelines
• Tests added (not required for documentation-only changes)
• Updates entries in docs/sphinx/source/reference (not required — API unchanged)
• Adds description in "what's new" (not required for small docstring improvements)
• New code is fully documented with numpydoc-compliant examples
• Pull request is nearly complete and ready for detailed review
• Maintainer: add labels and milestone

Address the documentation portion of #943
This pull request improves the documentation for
ModelChain.run_model_from_poa by adding a complete, runnable example to the
docstring.
Changes demonstrates:

1)Creating a simple PVSystem and Location

2)Creating a POA DataFrame with required columns

3)Running the model using run_model_from_poa

4)Ensures formatting and indentation follow pvlib’s numpydoc standards.
@cwhanse
I have done changes for PR2.

[Chirag3841]

@cwhanse
I have done changes in run_model_poa() method by adding example

[cwhanse]

@Chirag3841 this PR is stacked on top of the changes in #2601. Could you rebase the last commit 8eef3f3 onto pvlib's main? That way, this PR won't require you to duplicate any edits to #2601, and we can review in parallel.

[Chirag3841]

@cwhanse
Changes applied. Please review.