Relax posthog upper bound<6.0.0 to prevent installation conflicts.

[sipa-echo-ngbm]

Is your feature request related to a problem? Please describe.
I am encountering a dependency conflict that prevents me from installing deepeval. I'm always frustrated when I can't use the latest versions of other tools in my stack. Specifically, deepeval==3.9.6 restricts the posthog dependency to <6.0.0. However, my project requires posthog==7.9.6 (a much newer version).

Because of this strict upper bound, modern package managers like uv fail to resolve the dependencies, making it impossible to add deepeval to a project that is already utilizing current versions of PostHog.

Describe the solution you'd like
I would like deepeval to update its posthog dependency requirement to support version 7.x.x (e.g., posthog>=5.4.0,<8.0.0 or similar), assuming there are no breaking changes in the newer PostHog SDK that negatively impact deepeval's telemetry/tracking.

Describe alternatives you've considered

• Downgrading PostHog: I considered downgrading my project's posthog dependency to a 5.x.x version, but this would break my application which relies on newer PostHog features.
• Forcing the installation: Using the --frozen flag in uv or --no-deps in pip to skip locking, but this is a hacky workaround that could lead to unexpected runtime errors and unstable environments.
• Forking the repo: Forking deepeval to manually bump the dependency constraint, which I'd prefer to avoid so I can stay on the official release track.

Additional context
Here is the exact terminal output when attempting to add the package using uv:

>uv add deepeval==3.9.6
  x No solution found when resolving dependencies:
  `-> Because deepeval==3.9.6 depends on posthog>=5.4.0,<6.0.0 and your project depends on deepeval==3.9.6, we can conclude that your project depends on posthog>=5.4.0,<6.0.0.
      And because your project depends on posthog==7.9.6, we can conclude that your project's requirements are unsatisfiable.
  help: If you want to add the package regardless of the failed resolution, provide the `--frozen` flag to skip locking and syncing.