更好的 PGP 加密消息的检测方法

[TransparentLC]

目前是使用这种简单的检测方法：

https://github.com/TransparentLC/LiteLoaderQQNT-PGP-Encryption/blob/938b4d8b9bfef3b224a569e912669949de0bbe3a/src/renderer/index.ts#L41-L44

之前也在 https://github.com/TransparentLC/LiteLoaderQQNT-PGP-Encryption/issues/1#issuecomment-2531409584 考虑过使用一个更详细的正则表达式检测整个消息，但是发现可能会 ReDoS，所以也没有实装。

// 每一行后面有一个空格
`-----BEGIN PGP MESSAGE----- 

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=xxxx 
-----END PGP MESSAGE----- `.match(/^-----BEGIN PGP MESSAGE-----\s*(?:.+?:.*\n)*\s*\n(?:[A-Za-z\d+\/]*\n?)*={0,2}\n=(?:[A-Za-z\d+\/]{4})?\n\s*-----END PGP MESSAGE-----\s*$/);