Add support for NEP-413 message signature verification

[denbite]

Have you read the Contributing Guidelines?

• I have read the Contributing Guidelines on issues.

Description

Right now, developers who want to verify NEP-413 message signatures have to write a lot of custom boilerplate. There’s no out-of-the-box helper in @near-js/*, which makes the process harder than it should be.

Has this been requested on GitHub Discussions?

No response

Motivation

The goal is to provide developers with a straightforward way to validate signed messages against public keys without relying on repetitive, custom boilerplate.

API design

We’d love to hear community proposals on what this API should look like, please suggest your preferred approach directly here

Self-service

• I'd be willing to contribute and develop this feature myself.

[Gmin2]

I think we should keep NEP‑413 verification in @near-js/signers next to signNep413Message, and expose two minimal helpers: verifyNep413MessageSignature(params, signature, publicKey):
boolean and a convenience verifySignedNep413Message(params, signed): boolean. The params should mirror the signing schema (message, recipient, nonce: Uint8Array of exactly 32 bytes, optional callbackUrl),
serialize with the same borsh struct and the u32 prefix hash with SHA‑256, and verify via PublicKey.verify. These functions return a boolean for validity and only throw for programmer errors. If needed later, we can add an advanced

cc @denbite