Fix: properly render P-Median model formulation in docs (#466)

[Abhishek-Dimri]

This PR fixes the incorrect rendering of the P-Median mathematical formulation in the documentation site.

• Reformatted the equations using display math blocks for compatibility with Sphinx/Markdown.
• Ensures better readability and consistency across platforms (Jupyter, ReadTheDocs, etc.).

Before-

and

After-

and

Note:
Some small phrasing changes were made for clarity and readability in the documentation (e.g., "Index referencing demand nodes" vs. "Index referencing nodes of the network as demand"). If you prefer the original phrasing, let me know, and I'm happy to revert it.

Fixes #466

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.8%. Comparing base (13ca45e) to head (1a2cbe5).
Report is 7 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #483   +/-   ##
=====================================
  Coverage   77.8%   77.8%           
=====================================
  Files         27      27           
  Lines       2638    2638           
=====================================
  Hits        2053    2053           
  Misses       585     585           

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[martinfleis]

Thanks! Much appreciated!

[jGaboardi]

Thanks!