populate_config prefixed "file://" onto the result of pathname2url, which
already returns a leading "///" on Windows. Three slashes plus two gives
file://///C:/..., an empty authority that urlopen reads as a UNC path, so
every URIRequirement failed there before the file was ever opened. That
covers --single-location, --yara-file, --yara-compiled-file, --strings-file,
--isf and volshell's --script.
pathlib's as_uri produces the same string as the current code on POSIX for
every supported Python version, and the correct one on Windows, including
for UNC paths. It also sidesteps the Python 3.14 rewrite of pathname2url,
which gives POSIX the same leading "///" that Windows always returned.
The two other places in the codebase that build file URLs,
URIRequirement.location_from_file and volshell's run_script, were already
correct; this was the only one assembling the scheme by hand.
