Clarify docs for parse_number() behavior with non-numeric characters

[sbearrows]

Developed from #1415

We might want to clarify the docs for how parse_number() handles special characters found after the first valid number. Right now the docs for parse_number() says:

This drops any non-numeric characters before or after the first number.

I think this is a bit confusing since there could be valid numbers after the first number, for example:

readr::parse_number("132aa000")
#> [1] 132

^{Created on 2022-08-25 by the reprex package (v2.0.1.9000)}
Maybe something like:

"This parses the first number it finds, dropping any non-numeric characters before the first number and all characters after the first number."