fix(WAProto): Handle string values in long fields during JSON serialization

[jlucaso1]

Fixes a TypeError: this.isZero is not a function that can occur when serializing a WebMessageInfo object to JSON.

The error happens in a specific edge case where a field defined as a long in the protobuf schema (like fileLength in an ImageMessage) is incidentally assigned a string value instead of a Long object or a number.

[whiskeysockets-bot]

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📦 To test this PR locally:

# NPM
npm install @whiskeysockets/baileys@WhiskeySockets/Baileys#fix-iszero-serialization

# Yarn (v2+)
yarn add @whiskeysockets/baileys@WhiskeySockets/Baileys#fix-iszero-serialization

# PNPM
pnpm add @whiskeysockets/baileys@WhiskeySockets/Baileys#fix-iszero-serialization

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

[purpshell]

resolve conflicts

[github-actions]

This PR is stale because it has been open for 14 days with no activity. Remove the stale label or comment or this will be closed in 14 days

[vinikjkkj]

how to reproduce?

[github-actions]

This PR is stale because it has been open for 14 days with no activity. Remove the stale label or comment or this will be closed in 14 days