don't mutate properties or options

[lukepighetti]

:bulb: Motivation and Context

I was sending an analytics payload to multiple providers, Posthog was mutating the properties map and adding in $screen_name

:green_heart: How did you test it?

:pencil: Checklist

• [ ] I reviewed the submitted code.
• [ ] I added tests to verify the changes.
• [ ] I updated the docs if needed.
• [ ] No breaking change or entry added to the changelog.

[marandaneto]

@lukepighetti would you mind adding a CHANGELOG entry?