Use 'Enumerate Package Versions' request for NuGet version enumeration

[Enumerate Package Versions](https://learn.microsoft.com/en-us/nuget/api/package-base-address-resource#enumerate-package-versions) returns just the array of the versions of a package, as opposed to the endpoint we currently use which lists all the package info (but can also return some batch thing for big queries).

e.g:
Current: https://api.nuget.org/v3/registration5-semver1/newtonsoft.json/index.json
New: https://api.nuget.org/v3-flatcontainer/newtonsoft.json/index.json