Add Tenzro method specification

[hilarl]

Specifies the Tenzro MPP method: HTTP 402 challenge / credential / receipt flow settling natively on the Tenzro Ledger L1 in TNZO or any Tenzro-Ledger-resident asset (wTNZO ERC-20/SPL pointers, CIP-56 holdings).

Reference implementation: https://github.com/tenzro/tenzro-network/tree/main/crates/tenzro-payments/src/mpp

Highlights:

• Mandatory hybrid Ed25519 + ML-DSA-65 signatures on every credential and voucher
• TDIP DID binding with optional KYC-tier gating
• DelegationScope + runtime SpendingPolicy enforcement at challenge-time and session-close
• Streaming via micropayment channels (MppVoucher with cumulative-amount semantics)
• Settlement target options: block_inclusion (~2s) or block_finality (HotStuff-2, ~6-12s)

Engaging @tempoxyz and Stripe maintainers for review.