Add support for dataframe and arrow table in add_entities

[FroggoLight]

Allows client to call add_entities with either dataframe or arrow table without having to call individual add_attributes for all of the data columns.

[codecov]

Codecov Report

❌ Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.69%. Comparing base (a06c741) to head (4eb1dce).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lenskit/data/builder.py	91.30%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #907   +/-   ##
=======================================
  Coverage   89.69%   89.69%           
=======================================
  Files         223      223           
  Lines       15476    15499   +23     
=======================================
+ Hits        13881    13902   +21     
- Misses       1595     1597    +2     

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[mdekstrand]

Good work! There are some subtle edge cases for different Pandas index layouts we need to handle, and documentation to add, but otherwise it looks sound.