feat: add opt-in automatic recovery for promise and callback APIs

[ShiriNmi1520]

Summary

This PR adds a generic, opt-in recovery mechanism to amqplib for both public APIs:

• Promise API (require('amqplib'))
• Callback API (require('amqplib/callback_api'))

Recovery is enabled only when connect(..., { recovery: ... }) is provided, so the default behaviour remains unchanged.

Motivation

Fix #25

What changed

• Added shared recovery engine: lib/recovery.js
• Wired recovery into:
  • channel_api.js
  • callback_api.js
• Added docs in README.md for usage/options/events
• Added unit tests in test/recovery.js

Recovery options

• initialDelay
• maxDelay
• factor
• jitter
• maxRetries (also accepts maxAttempts)
• setup(model, client[, done]) called after each successful connect/reconnect

Mermaid sequence chart

sequenceDiagram
    autonumber
    participant App
    participant Client as amqplib (recovering client)
    participant Broker as RabbitMQ

    App->>Client: connect(url, { recovery })
    Client->>Broker: open TCP + AMQP handshake
    Broker-->>Client: open-ok
    Client->>Client: run recovery.setup(...)
    Client-->>App: emit "connect"

    Note over Broker,Client: normal operation

    Broker-x Client: socket/connection closed
    Client-->>App: emit "disconnect"
    Client-->>App: emit "reconnectScheduled"

    loop retry with backoff+jitter
        Client->>Broker: reconnect + handshake
        alt success
            Broker-->>Client: open-ok
            Client->>Client: run recovery.setup(...)
            Client-->>App: emit "connect"
        else failed and retries remain
            Client-->>App: emit "connectFailed"
            Client-->>App: emit "reconnectScheduled"
        end
    end

    alt retries exhausted
        Client-->>App: emit "reconnectFailed"
    end

Loading

Backward compatibility

• No behavior change unless recovery is explicitly configured.

Notes / limitations

• This provides connection-level recovery and setup replay.
• It does not guarantee transparent replay of in-flight channel operations across disconnects.

[cressie176]

Thank you for this @ShiriNmi1520, it looks like a very comprehensive piece of work. I've have some time off next week and will review.