sdk: strict validation and typed errors for exportReceipt output

[karagozemin]

Summary

Harden exportReceipt / serializeReceipt in packages/sdk so malformed or partial on-chain state produces a typed error rather than an incomplete receipt.

Motivation

Receipts are the verifiable artifact users rely on. Silently emitting an incomplete receipt undermines the 'protocol owns fairness' guarantee.

Acceptance criteria

• Missing/invalid fields raise a dedicated error class.
• Receipt schema version is always present and validated.
• Round-trip test (serializeReceipt → parseReceipt → verifyReceipt).
• Tests for at least three malformed-input cases.

[Fury03]

Hi, Maintainer I can work on this.
Kindly assign