feat: allow proposed issuer to reject pending transfer

[Topmatrixmor2014]

#363 Add reject_issuer_transfer so the proposed new_issuer can explicitly decline a pending transfer
Repo Avatar
RevoraOrg/Revora-Contracts
Description
The two-step issuer transfer flow lets the old issuer cancel_issuer_transfer, but the proposed new_issuer can only decline passively (by never accepting until expiry). Add reject_issuer_transfer(new_issuer, namespace, token) so the proposed party can immediately and verifiably decline, freeing the offering for a new proposal and emitting an auditable event.

Requirements and context
Must be secure, tested, and documented
Should be efficient and easy to review
Relevant code: src/lib.rs (propose_issuer_transfer, accept_issuer_transfer, cancel_issuer_transfer, find_pending_transfer_for_new_issuer)
Only the pending new_issuer may reject; emit a dedicated event
Suggested execution
Fork the repo and create a branch
git checkout -b feat/reject-issuer-transfer
Implement changes
Reuse find_pending_transfer_for_new_issuer to locate the offering
Require new_issuer.require_auth() and remove PendingIssuerTransfer
Emit a new iss_rej event with (old_issuer, new_issuer)
Validate security and correctness assumptions
Test and commit
Run tests
cargo test
Cover edge cases
Reject by wrong address, reject when no pending, re-propose after reject
Include test output and security notes
Example commit message
feat: allow proposed issuer to reject pending transfer

Guidelines
Minimum 95 percent test coverage
Clear documentation
Timeframe: 96 hours
closes #363