## About The Pull Request
This PR reimplements https://github.com/tgstation/tgstation/pull/71538
atop `master`. Quoting the original PR:
> Every `icon_exists()` call will cache the entire file. Past me didn't
realise _why_ file opts were so expensive, but I do now. This is
immeasurably slower on a single call, and _significantly_ faster on
subsequent calls to the same file.
I attempted to handle some of the review comments that were posted
there, by splitting screaming functionality into its own proc.
* `if(icon_state in icon_states(file))` and `if(!(icon_state in
icon_states(file)))` were refactored to use `icon_exists(file,
icon_state)`.
* Where screaming was seemingly wanted (and where there wasn't a more
descriptive error inside the `if` block), I refactored them to use
`icon_exists_or_scream(file, icon_state)`
* The exception to the above was under
`/datum/unit_test/turf_icons/Run()` and
`/datum/unit_test/worn_icons/Run()`, where `icon_states()` was being
passed a mode flag. Given that this is only used in unit tests (where
performance isn't a priority), I opted to leave these be.
Additionally, I revised the documentation comment for
`/proc/icon_exists()`, as I felt it was a bit vague currently.
## Why It's Good For The Game
https://youtu.be/Z9G1Mf6TZRs
## Changelog
No player-facing changes (hopefully).
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Co-authored-by: SyncIt21 <110812394+SyncIt21@users.noreply.github.com>