feat: add UniFFI endpoint and background driver

[deepso7]

Summary

• add a UniFFI-facing endpoint wrapper with validated configuration, lifecycle management, commands, queries, and typed events
• add the interruptible background driver with bounded event carry, cancellation filtering, keepalive, overflow accounting, and panic isolation
• add direct-loopback and relay-backed integration coverage, including ordering, load, shutdown, listener panic, and callback/query handoff regressions
• document native ownership, lifecycle, address semantics, discovery constraints, queue bounds, and host-wrapper responsibilities
• pin the Android BoringSSL allocator-hook fix pending an upstream crates.io release

Verification

• just test
• just clippy
• just check-nostd
• just docs
• cargo +1.88 check --workspace --all-targets
• just fuzz 30
• iOS physical-device runtime spike
• Android physical-device runtime spike
• direct loopback and relay-backed FFI integration tests

Notes

• the FFI ABI and generated binding shape remain pre-1.0 and unstable
• host-side TypeScript/Swift/Kotlin queues must define their own bounds; the native carry limit does not bound host queues
• the temporary boring/boring-sys patch should be removed after an upstream release includes fix(boring-sys): localize allocator hooks on Android cloudflare/boring#518

---

Summary by cubic

Adds a UniFFI-based minip2p-ffi endpoint and an interruptible background driver to embed minip2p safely in mobile apps. Includes validated config, lifecycle controls, typed events, hardened pubsub deduplication, and stabilized end-to-end tests over loopback and relay.

• New Features

  • New crate minip2p-ffi exposing a UniFFI endpoint for React Native, Swift, and Kotlin, plus identity and relay-address helpers.
  • Validated construction; commands and queries; typed events for swarm, NAT, pubsub, and signed discovery.
  • Background driver with bounded event carry, cancellation filtering, keepalive, overflow accounting, and panic isolation; start/stop with bounded waits and listener callbacks.
  • Integration tests for direct loopback and relay paths, covering ordering, load, shutdown, and listener-panic cases; stabilized loopback CI timing; README on lifecycle and ownership.
  • Hardened pubsub dedup so unsigned messages cannot suppress later signed messages; added Floodsub and Gossipsub tests.

• Dependencies

  • Added uniffi pinned to =0.31.0 to match host tooling.
  • Temporarily patched boring and boring-sys to a git revision to fix the Android allocator hook; remove after the upstream crates.io release.

^{Written for commit d735d96. Summary will update on new commits.}

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