docs(rust): Update DataFrame construction docs for Column

[uurl]

Closes #24931.

Summary

• Updates the DataFrame Rust documentation to describe construction from Vec<Column> instead of Vec<Series>.
• Keeps the existing example, which already uses Column::new.

Validation

• git diff --check
• cargo fmt --all --check
• cargo test -p polars-core --doc

AI disclosure

1. I used AI to help identify the narrow documentation scope and review the PR text.
2. I confirm that I have reviewed all changes myself, and I believe they are relevant and correct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.40%. Comparing base (4808230) to head (c77d8cd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #27541      +/-   ##
==========================================
- Coverage   81.42%   81.40%   -0.02%     
==========================================
  Files        1837     1837              
  Lines      255165   255165              
  Branches     3179     3179              
==========================================
- Hits       207759   207725      -34     
- Misses      46582    46616      +34     
  Partials      824      824              

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