renderer: cache workspace fullscreen windows

[NotPppp1116]

cache each workspace's fullscreen window as a weak reference and keep it synchronized across fullscreen transitions, workspace moves, unmaps, and recovery paths
make fullscreen window lookup O(1) while preserving layout-managed fullscreen handling
simplify the fullscreen renderer path: avoid temporary smart-pointer vectors, use the cached fullscreen window in the common path, and keep the broader scan only while other workspaces animate avoid smart-pointer copies across hot renderer helpers and blur predicates by passing handles as const&
cache repeated monitor workspace IDs locally in shouldRenderWindow

[github-actions]

Hello and thank you for making a PR to Hyprland!

Please check the PR Guidelines and make sure your PR follows them.
It will make the entire review process faster. :)

If your code can be tested, please always add tests. See more here.

beep boop, I'm just a bot. A real human will review your PR soon.

[vaxerski]

@codex review please

[vaxerski]

this is iffy fullscreen state is quite flaky I dont like it in general but ugh

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 13a05ba1f1

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".