Consider supporting runtime install without sdk

Not sure if this is something the plugin could (or should) support, but the full dotnet SDK + runtime is almost 600MB. Sometimes you only need the runtime support.

There are separate download links which can retrieve just the runtime (less than 100MB) when only that is needed.

$ dua --format metric /root/.version-fox/cache/dotnet/v-8.0.8/dotnet-8.0.8

   4.10 KB LICENSE.txt
  69.63 KB dotnet
  98.30 KB ThirdPartyNotices.txt
 290.82 KB host
 368.64 KB sdk-manifests
   6.10 MB templates
  90.46 MB packs
  96.56 MB shared
 395.64 MB sdk
 589.59 MB total

It looks like the plugin already has the logic to find the correct direct-link, so it might be able to resolve this for runtime as well:

# https://dotnet.microsoft.com/en-us/download/dotnet/thank-you/runtime-aspnetcore-8.0.8-linux-x64-binaries
# The above URL would respond with page for real direct-link + checksum:
export DOTNET_RUNTIME_8_URL=https://download.visualstudio.microsoft.com/download/pr/648de803-0b0c-46bc-9601-42a94dae0b41/241fd17cee8d473a78675e30681979bb/aspnetcore-runtime-8.0.8-linux-x64.tar.gz

$ mkdir /tmp/dotnet-runtime-8
$ curl -fsSL "${DOTNET_RUNTIME_8_URL}" | tar -xz -C /tmp/dotnet-runtime-8

# `ASP.NET Core Runtime` (24MB) includes `.NET Runtime` (72MB):
$ dua --format metric dotnet-8
   4.10 KB LICENSE.txt
  69.63 KB dotnet
  98.30 KB ThirdPartyNotices.txt
 290.82 KB host
  96.56 MB shared
  97.02 MB total

Other feedback (this might be vfox specific) was that I could not use vfox install dotnet@8 or vfox install dotnet@8.0. The exact version (8.0.8 at this time) was required, even though vfox install / vfox search knows the available versions for interactive selection.

Start with the plugin's existing direct-link resolution and the vfox install/search entry points mentioned in the issue. Determine how runtime-only downloads and shorthand versions such as 8 or 8.0 should be handled; done means those install requests can select the appropriate runtime without requiring the full SDK.