Skip Inactivity Only Measure Cursor Movement Not Keyboard Usage

Bug Description

Skipping inactivity only seems to factor in cursor movement not keyboard movement. A user wrote in that makes games and at least one of them can be primarily used with just a keyboard. I was able to replicate it and for ~5-10 minutes of playing with just the keyboard it skips inactivity that is actually activity and resumes for a short bit after moving the mouse in the middle of the play time.

How to reproduce

Probably easily reproducible (haven't confirmed) on any page with session replay

1. Use up/down/left/right keys for a couple minutes on any page where session replay is enabled
2. Move mouse at the beginning for 10 seconds, then sometime in the middle, then at the end
3. Watch the session replay with skip inactivity enabled

Additional context

The easy answer is turn off skip inactivity but this seems like a worthwhile improvement to make if we can, I've run into a few companies using PostHog with games lately so I have to imagine there's some value there.

Debug info

- [x] PostHog Cloud, Debug information: [please copy/paste from https://us.posthog.com/settings/project-details#variables or https://eu.posthog.com/settings/project-details#variables]
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]

Start with the session replay behavior controlled by the “skip inactivity” option and reproduce the issue using only the arrow keys, with mouse movement at the beginning, middle, and end. Done means keyboard activity is treated as activity so replay does not skip those periods; no specific files or tests are named in the issue.