Refactor SenderKeyMessage to use static signature length

[Kunboruto20]

This PR refactors the SenderKeyMessage class to make it easier to work with and more consistent across environments.
Changes include:
Internal fields now consistently use Uint8Array instead of mixing Buffer and Uint8Array, making it compatible with both Node and browsers.
Added a toJSON() method for quick inspection and logging of the message content.
Added verifySignatureAsync() for async-friendly signature verification that returns a boolean instead of throwing.
Retained the original verifySignature() behavior for backwards compatibility.
Introduced helper methods for safely handling base64/hex conversions and concatenating byte arrays.

[whiskeysockets-bot]

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Tested and working ✅

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📦 To test this PR locally:

# NPM
npm install @whiskeysockets/baileys@Kunboruto20/Baileys#patch-1

# Yarn (v2+)
yarn add @whiskeysockets/baileys@Kunboruto20/Baileys#patch-1

# PNPM
pnpm add @whiskeysockets/baileys@Kunboruto20/Baileys#patch-1

If you encounter any issues or have feedback, feel free to comment as well.

[jlucaso1]

One more time? #2220 (comment)

[Salientekill]

One more time? #2220 (comment)

Is there anything relevant that could be used? Extracted into a separate PR that makes sense?

[github-actions]

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