dnx doesn't fall back to local cache when network is unavailable

### Describe the bug
If you run `dnx` without a network connection, the command currently totally fails connecting to the nuget server, even if there there are compatible cached versions.

If there's no network connection, I'd expect dnx to fall back to whatever matching version it can find in the local nuget cache, rather than failing outright.

### To Reproduce
1. Install a tool e.g. `dotnet dnx --yes dotnet-ef`
2. Pull your network cable / Turn on Flight mode
3. Try to re-run the tool

### Exceptions (if any)
No such host is known. (nuget.org:443)

### Further technical details
details of dotnet --info

.NET SDK:
Version: 10.0.100-preview.7.25380.108
Commit: 30000d883e
Workload version: 10.0.100-manifests.8bb6be96
MSBuild version: 17.15.0-preview-25380-108+30000d883

Runtime Environment:
OS Name: Windows
OS Version: 10.0.26100
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\10.0.100-preview.7.25380.108\

.NET workloads installed:
There are no installed workloads to display.
Configured to use workload sets when installing new manifests.
Workloads are configured to install and update using workload versions, but none were found. Run "dotnet workload restore" to install a workload version.

Host:
Version: 10.0.0-preview.7.25380.108
Architecture: x64
Commit: 30000d883e

.NET SDKs installed:
8.0.413 [C:\Program Files\dotnet\sdk]
9.0.304 [C:\Program Files\dotnet\sdk]
10.0.100-preview.7.25380.108 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 10.0.0-preview.7.25380.108 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 10.0.0-preview.7.25380.108 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 9.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 10.0.0-preview.7.25380.108 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
x86 [C:\Program Files (x86)\dotnet]
registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
Not set

global.json file:
Not found

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