No error message is provided when there is a Network Failure

Reproduction steps

Use libgit2sharp in a bad network place

Expected behavior

Throw an exception that explicitly mentions network failure

Probably it's a good idea to handle situations where wifi signal is not strong or network failure. We could also handle this gracefully.

Actual behavior

Throws LibGit2Sharp.LibGit2SharpException saying

No error message has been provided by the native library

Stack trace,

Unhandled exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> LibGit2Sharp.LibGit2SharpException: No error message has been provided by the native library
   at LibGit2Sharp.Core.Ensure.HandleError(Int32 result)
   at LibGit2Sharp.Core.Ensure.ZeroResult(Int32 result)
   at LibGit2Sharp.Core.Proxy.git_remote_fetch(RemoteHandle remote, IEnumerable`1 refSpecs, GitFetchOptions fetchOptions, String logMessage)
   at LibGit2Sharp.Commands.Fetch(Repository repository, String remote, IEnumerable`1 refspecs, FetchOptions options, String logMessage)
   at LibGit2Sharp.Commands.Pull(Repository repository, Signature merger, PullOptions options)
   at GitUtil.Program.Main(String repoPath, String action, String filePath) in D:\git_ws\GitUtil\Program.cs:line 84
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Span`1& arguments, Signature sig, Boolean constructor, Boolean wrapExceptions)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
   at System.CommandLine.Invocation.ModelBindingCommandHandler.InvokeAsync(InvocationContext context)
   at System.CommandLine.Invocation.InvocationPipeline.<>c__DisplayClass4_0.<<BuildInvocationChain>b__0>d.MoveNext()
--- End of stack trace from previous location ---

Version of LibGit2Sharp (release number or SHA1)

0.27.0-preview-0158 and earlier

Operating system(s) tested; .NET runtime tested

Win 10, .Net SDK 6.0.101

Start at Core.Ensure.HandleError and follow the error path through Proxy.git_remote_fetch, Commands.Fetch, and Commands.Pull. Reproduce the bad-network fetch described in the issue and inspect how native errors are surfaced. Done means a network failure produces an exception with an explicit, useful network-related message instead of the empty native-library message.