Function signBundle

signBundle(
    bundle: Bundle,
    pair: KeyPair,
    opts?: { signedAt?: string },
): Promise<SignatureBlock>
Sign the bundle's canonical content with the keypair's private key. Returns a SignatureBlock ready to embed in the .iflx envelope.

signedAt defaults to new Date().toISOString(); pass an explicit value for deterministic test output.
Parameters
- bundle: Bundle
- pair: KeyPair
- Optionalopts: { signedAt?: string }
Returns Promise<SignatureBlock>