Consider using SafeHandle in Libgit2Object instead of void*

We've had a couple of bug reports against dotnet/runtime with rarely-reproduceable crashes coming from libgit2sharp. We believe that one possible reason could be an interop anti-pattern in Libgit2Object - void*/IntPtr representation of a native handle that can be freed in finalizer. E.g. in this case the finalizer in Libgit2Object may end up calling native free here (and other overloads).

The reason why it's called an anti-pattern can be explained by a short repro in this issue: https://github.com/dotnet/runtime/issues/103522 and a general solution is to use SafeHandle for such handles. Also, see https://learn.microsoft.com/en-us/dotnet/standard/native-interop/best-practices

Reproduction steps

Expected behavior

Actual behavior

Version of LibGit2Sharp (release number or SHA1)

Operating system(s) tested; .NET runtime tested

Inizia in LibGit2Sharp/Core/Handles/Libgit2Object.cs intorno alla riga 88, quindi traccia il finalizer e gli overload di liberazione nativa in LibGit2Sharp/Core/Handles/Objects.cs intorno alle righe 502-505. Confronta questi percorsi di ownership con le linee guida di SafeHandle e i report di runtime collegati. Il lavoro è completato quando i percorsi rilevanti del ciclo di vita degli handle nativi sono rappresentati e liberati in modo sicuro, senza la race del finalizer segnalata.