fix: Cast empty lists and lists of only nulls without an inner dtype

[petrosbar]

Fixes #15523

When building a Series of lists without specifying an inner dtype, if there's any empty list, construction will panic. The reason is that in AnyValue::List(b), if b is empty, its dtype is Null regardless of the dtype of the other lists.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.40%. Comparing base (0c37ead) to head (01064c3).
Report is 2238 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15525   +/-   ##
=======================================
  Coverage   80.39%   80.40%           
=======================================
  Files        1264     1264           
  Lines      165421   165434   +13     
=======================================
+ Hits       132994   133019   +25     
+ Misses      32427    32415   -12     

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[codspeed-hq]

CodSpeed Performance Report

Merging #15525 will improve performances by 16.33%

_{Comparing petrosbar:anyvalue-empty-list (01064c3) with main (d11da5e)}

Summary

⚡ 1 improvements
✅ 20 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	petrosbar:anyvalue-empty-list	Change
⚡	test_windows_not_cached	3.6 s	3.1 s	+16.33%