fix(player): support current signature and nsig extraction paths

[chadacious]

Fixes #1146

Summary

This updates player extraction to support the current signature and nsig patterns used by newer YouTube player variants.

What changed

• stop stripping side-effect initializers when building extracted player scripts
• preserve assignment/prototype dependency chains needed by current player helpers
• detect current signature helpers semantically instead of relying on the older hard-coded matcher shape
• derive nsig extraction from the same URL-helper class used by the matched signature helper

Notes

This was validated against multiple player ids, including:

• 6c5cb4f4
• 56211dc2
• 99f55c01
• ecc3e9a7
• 05540cb0
• 9f4cc5e4

and confirmed with real playback for both standard and purchased content in downstream integration testing.

Motivation

Recent player variants no longer match the older extraction assumptions:

• some helpers are attached through prototype/member assignment chains
• current signature helpers use a different structural shape
• stripping side-effect initializers can remove code required for nsig evaluation

This patch updates the extractor and matchers to handle those cases while keeping the external decipher API unchanged.

[ziluotian]

When parsing this video (0P4A1K4lXDo) in the browser, the following message appears:

exportedVars.rawValues is not a function

[ziluotian]

When parsing this video (0P4A1K4lXDo) in the browser, the following message appears:
Script: https://www.youtube.com/s/player/6c5cb4f4/player_es6.vflset/zh_CN/base.js
Failed to extract signature decipher function., Failed to extract n decipher function., exportedVars.rawValues is not a function

Simulating a mobile phone in the browser allows for normal parsing.
Script: https://m.youtube.com/s/player/6c5cb4f4/player-plasma-ias-phone-zh_CN.vflset/base.js

[ashleyirispuppy143]

seems like music videos/topic channel content dont work with playback someetimes the rest work fine!

[br0k3x]

when will this be merged?

[ashleyirispuppy143]

when will this be merged?

i think luan is working on a better fix himself. n-sig stuff is fine but the sig stuff isn't with this PR.

[absidue]

Superseded by #1152