TimestampSigner.unsign does not raise SignatureExpired when the token was signed in the future

TimestampSigner.unsign does not raise SignatureExpired when the token was signed in the future: a task in repo2rlenv-swe-next (Harbor dataset). When a token is signed at a future time (relative to when unsign is called), the computed age is negative. Currently, unsign does not raise any error in…