Clarify benefits of factory methods in Module 2

[ecomodeller]

The static methods section in Module 2 shows how to create factory methods but could better explain when and why to use them.

Current state

The notes mention it's "less cumbersome" to create instances, but the pedagogical value could be stronger.

Suggested improvements

1. Name the pattern - Use the term "factory method" or "alternative constructor" so students can recognize and search for it

2. Explain the "why" - Python doesn't support multiple __init__ signatures, so factory methods provide multiple construction paths with semantic clarity

3. Add stdlib examples from datetime:

   • datetime.fromtimestamp()
   • datetime.fromisoformat()
   • date.fromordinal()

4. Add examples from polars:

   • pl.read_csv(), pl.read_parquet(), pl.read_json() (module-level factories)
   • DataFrame.to_dict() → pl.from_dict() round-trip
   • pl.from_numpy(), pl.from_pandas()

These examples show the pattern is pervasive in well-designed Python APIs.