Fix lib name and version for AspNetCore and AI packages

[marandaneto]

Description

• PostHog.AspNetCore

  • Calls the core IPostHogClient.Capture(...).
  • It does not set/override $lib or $lib_version.
  • So events still report:
    • $lib = "posthog-dotnet" -> this should have been "posthog-aspnetcore"
    • $lib_version = PostHog core package version -> it should have its own version

• PostHog.AI

  • Adds AI-specific:
    • $ai_lib = "posthog-dotnet" -> this should have been "posthog-dotnet-ai" or something like that
  • Then calls the core IPostHogClient.Capture(...), so normal event properties still get:
    • $lib = "posthog-dotnet"
    • $lib_version = PostHog core package version
  • I don’t see an $ai_lib_version being set.

[marandaneto]

If we do this, we probably need to fix the usage report and feat flag backend SDK name matching

[marandaneto]

#314