feat: add owned runtime and synchronous payment transport

[parvahuja]

Runtime stack 3 of 5 · depends on #189 · next: #191

Summary

• add OwnedPaymentRuntime with one explicitly owned asyncio loop
• initialize and close managed method factories on that same loop
• expose sync/async lifecycle contexts and sync credential/event calls
• add SyncPaymentTransport with the same safety policy as the async transport
• share credentialed-response settlement between the sync and async transports

Why the synchronization remains

AnyIO owns the portal, loop thread, task submission, and managed async-context lifecycle. pympp keeps one condition for single-use lifecycle and active leases, plus futures for non-blocking async callers. Cancellation accounting, early sync claims, and conditional orphan cleanup each cover a reproduced portal-leak or close race. No Python thread or executor APIs are patched.

Review boundary

Owned-loop lifecycle and low-level sync HTTP only. No per-client or global HTTPX patching and no MCP changes.

Validation

• full suite: 899 passed, 41 skipped
• deterministic repeated-cancel, concurrent start/ledger, shutdown, factory-failure, and factory-reentry probes
• Ruff, formatting, and Pyright pass