Use a source-generated thread-safe randomizer with fallback to .NET 6.0's Random.Shared

[MarkCiliaVincenti]

No description provided.

[jodydonetti]

Hi Mark, thanks for the PR.
Sorry but as mentioned in the past, I don't add an extra dependency (even a MS one) to FusionCache lightly, less so in the main FusionCache package, less so if the dependency is 3rd party and even less so for an alternative random number generator used in exactly 1 line of code (jittering logic).
It's a tad bit too much honestly 😅