Function aggregate

aggregate(
    signingPackage: P256SigningPackage,
    signatureShares: Map<P256Identifier, SignatureShare<P256Sha256Impl>>,
    pubkeys: PublicKeyPackage<P256Sha256Impl>,
): P256Signature
Verifies each FROST(P-256, SHA-256) participant's signature share, and if all are valid, aggregates the shares into a signature to publish.

Resulting signature is compatible with verification of a plain Schnorr signature.

This function performs the final aggregation step of the FROST protocol:
1. Recomputes the binding factors and group commitment
2. Computes the challenge
3. Verifies each signature share against the corresponding verifying share
4. Aggregates all signature shares into the final signature
Parameters
- signingPackage: P256SigningPackage
  The signing package containing commitments and message
- signatureShares: Map<P256Identifier, SignatureShare<P256Sha256Impl>>
  Map of identifier to signature share
- pubkeys: PublicKeyPackage<P256Sha256Impl>
  The public key package
Returns P256Signature
The aggregated signature

Throws
Error if any signature share is invalid
- Defined in p256/src/index.ts:1425