Description

We should try to improve the performance / time before hiding elements with cosmetic filtering.

Steps to reproduce

1. Visit https://www.codeweavers.com/ with Shields up
2. Observe a few second delay before cookie consent banner is hidden

Actual result

4+ seconds before cookie consent is hidden

Expected result

Hide cookie consent faster

Reproduces how often

Easily reproduced

Brave version

Any

Device/iOS version

Any

Affected browser versions

• latest AppStore
• latest TestFlight
• previous TestFlight

Reproducibility

• with Brave Shields disabled
• in the latest version of mobile Safari

Miscellaneous information

Currently the SelectorsPollerScript.js is debouncing not throttling:
https://github.com/brave/brave-core/blob/b8b2288791d6e8c5160c0c7c9dc2c49f05bd5cfe/ios/brave-ios/Sources/Brave/Frontend/UserContent/UserScripts/Scripts_Dynamic/Scripts/Sandboxed/SelectorsPollerScript.js#L1067

This causes us to delay applying the stylesheet changes until a site stops mutating, despite us having a list of selectors we wish to hide. We should be able to adjust this logic to throttle instead of debounce to improve the delay before applying cosmetic filtering.

Some more info:
https://bravesoftware.slack.com/archives/C3GNZANPR/p1728083196381259?thread_ts=1727926087.911499&cid=C3GNZANPR