proxyfmu URI with `localhost` does not work on Windows platform

[davidhjp01]

Steps to reproduce:

Create an OspSystemStructure.xml with a simulator source URI e.g. proxyfmu://localhost?file=Spring.fmu .
This runs fine on Linux but crashes on Windows

[kyllingstad]

Need to check whether this is a libcosim issue (e.g. with the URI parser) or a proxyfmu issue, and in the latter case, move the issue report to the proxyfmu repo.