fix: prevent autoplay playback before play() is called

[TeapoyY]

Summary

This PR fixes a bug where disabling autoplay would cause videos to play for approximately 1 second before being paused, instead of preventing playback entirely.

Root Cause

In js&css/web-accessible/functions.js, the autoplayDisable() function was called inside the HTMLMediaElement.prototype.play override, but the pauseVideo() call was scheduled via setTimeout(0). By the time the callback ran, the video had already started playing (since play() returns a Promise that resolves asynchronously).

Fix

The fix restructures the autoplay prevention to check conditions BEFORE calling original.play():

1. Check conditions first: Before invoking the original play() method, we check if autoplay should be blocked based on storage settings (player_autoplay_disable, playlist_autoplay, channel_trailer_autoplay).
2. Pause synchronously: If autoplay should be blocked, we call video.pause() synchronously BEFORE play(), preventing any video playback.
3. Return resolved Promise: We return Promise.resolve() to satisfy callers without triggering the browser autoplay mechanism.

This ensures the video never starts playing in the first place, rather than pausing after the fact.

Issues Fixed

• Fixes Disabled autoplay pauses a second into video instead of immediately preventing playback #1461: Disabled autoplay pauses a second into video instead of immediately preventing playback
• Fixes The autoplay feature(not up next) on a new tab isn't working. #1851 (Bounty): The autoplay feature on a new tab is not working

Testing

The fix has been tested for:

• Direct URL navigation to watch pages
• Opening videos in new tabs
• Playlist pages with playlist_autoplay === false
• Channel homepage with channel_trailer_autoplay === false