fix: use to_backend_array() instead of asarray

[agoose77]

Succinctly, asarray is less powerful than to_backend_array(). It often goes through iterative type discovery, rather than leveraging our internal typed layouts. We should instead be using our internal to_backend_array().

[codecov]

Codecov Report

Merging #2592 (e5f6f78) into main (d3e494a) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

Files Changed	Coverage Δ
src/awkward/operations/ak_nan_to_num.py	98.21% <100.00%> (ø)

[jpivarski]

Okay to merge, and it looks like a simple enough change that you're done with it and I can merge it. Thanks!