Feature Request: group viewports to avoid too many values

Feature request

Is your feature request related to a problem?

Viewport sizes are treated too granularly (e.g., 1920×1080 vs. 1919×1080), causing users to be split across many tiny buckets.

Describe the solution you'd like

• Implement viewport grouping / bucketing so slightly different resolutions are merged (e.g., rounding widths/heights to the nearest 8-10–16px). This would make totals align with overall visitor counts and improve readability.

Describe alternatives you've considered

Define fixed viewports and doing a lookup on them.

Additional context

https://posthoghelp.zendesk.com/agent/tickets/42646 (moved to PostHog: https://us.posthog.com/project/2/support/tickets/44410)

Debug info

- [ ] PostHog Cloud, Debug information: [please copy/paste from https://us.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]

No files, tests, or entry points are named. Start by reviewing the linked Zendesk and PostHog support tickets, then clarify the bucketing rule and how it should compare with fixed viewports. Done means slightly different resolutions are merged while totals align with overall visitor counts and remain readable.