Adds length checks to Max and Min functions to provide clear,
explicit panic messages when called with empty slices, rather
than allowing confusing index-out-of-bounds panics.
Changes:
- Max: Added check for empty slice with "underscore.Max: empty slice" panic
- Min: Added check for empty slice with "underscore.Min: empty slice" panic
- Updated doc comments to document panic behavior
- Added TestMaxEmpty and TestMinEmpty to verify panic behavior
Impact:
- Better error messages for debugging
- Documented behavior prevents user surprises
- Non-breaking change (still panics, just with clearer message)
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Co-Authored-By: Claude <noreply@anthropic.com>
