Add Tempo session payments

[parvahuja]

Summary

• add the private-key TIP-1034 v2 client with a required raw-unit max_deposit and generic Store
• persist and replay channel opens, top-ups, and vouchers; recover validated snapshots and on-chain state
• handle sync and async HTTP/SSE controls on the exact request URI, including compressed streams
• serialize channel updates, enforce deposit caps, accept scoped operators, and reuse one 2D nonce lane per channel
• recover unknown sponsored opens/top-ups only from a finalized block hash with a fail-closed EIP-1898 state read
• keep async channel-store state on the shared runtime loop and add built-wheel session API coverage

Private-key scope only: no access keys, WebSockets, close/server manager, or bootstrap preflight.

Stacked on #170. Depends on merged tempoxyz/pytempo#69 and its next PyPI release before merge.

Validation

• full stacked Python 3.13 suite with exact pytempo ci: add CI Gate job for branch protection #69: 894 passed, 41 skipped
• focused session/SSE suite: 33 passed
• ruff check, ruff format --check, and pyright with zero errors
• wheel and sdist builds plus strict twine checks
• clean Python 3.12 pympp + pytempo wheel-to-wheel install and session construction smoke
• independent correctness/concision review completed with no remaining findings

PyPI still serves pytempo 0.5.1, which lacks encode_for_signing(). After the #69 change is released, this PR must raise the pytempo minimum and rerun the package matrix. Protocol-shaped HTTP/SSE flows are covered locally; a live TIP-1034 server was not exercised. The PR remains draft.