Use xml_find_int() over xml_find_num()

[MichaelChirico]

Recent (Dec. 2023) xml2 v1.3.6 exports xml_find_int() which basically does as.integer(xml_find_num(.)).

#2439 found that all of our internal usages work just like that -- convert xml_find_num() output to integer. Therefore we should switch everything to the new function.

Tried this in #2439 directly but it caused some issues. Anyway, it might be best to let the hot-off-the-presses {xml2} release simmer a bit before we include the functionality, so I'll leave this to the next release.

[MichaelChirico]

The core issue is that xml_find_int() needs to be more robust to missing input:

r-lib/xml2#435

This is an illustrative test:

lintr/tests/testthat/test-xml_nodes_to_lints.R

Line 101 in 72eeefd

xp_invalid <- "number(./DOES-NOT-EXIST/@col1)"

With xml_find_num(), we get NaN back and handle it. But xml_find_int() throws an error when it gets NaN. Need to handle this upstream first.