Add automatic publisher confirmation tracking with async API

Traditional publisher confirms in the Java client require manual tracking
of sequence numbers and correlation of Basic.Return messages. This makes
per-message error handling complex and provides no built-in async pattern.

This change introduces automatic publisher confirmation tracking with a
`CompletableFuture`-based API, following the design of the .NET client's
publisher confirmation implementation. When enabled via `ChannelOptions`,
the library automatically tracks each message's confirmation status and
completes futures when the broker sends Basic.Ack, Basic.Nack, or
Basic.Return.

New API methods:
- `Channel.basicPublishAsync()` - Returns `CompletableFuture<Void>` that
  completes when broker confirms the message
- `Connection.createChannel(ChannelOptions)` - Creates channel with
  publisher confirmation tracking enabled

New classes:
- `ChannelOptions` - Configuration for channel creation with tracking
  settings and optional limit on outstanding confirmations
- `PublishException` - Exception thrown when message is nack'd or returned,
  with full details including sequence number and routing information
- `InternalException` - Exception for internal library bugs with GitHub
  issue reporting instructions

The implementation adds a sequence number header (`x-java-pub-seq-no`) to
each tracked message, allowing correlation of Basic.Return responses with
specific messages. When `maxOutstandingConfirms` is set, `basicPublishAsync()`
blocks if the limit is reached, providing backpressure to prevent unbounded
memory growth.

The feature is opt-in and maintains full backward compatibility. Existing
`basicPublish()` and `waitForConfirms()` methods remain unchanged.

Author: lukebakken

RUNNING_TESTS.md

@@ -88,14 +88,26 @@ top-level directory of the source tree:
        -Dit.test=DeadLetterExchange
 ```
 
+* To run a single test class:
+
+```
+./mvnw verify -Dit.test=Confirm
+```
+
+* To run a specific test method within a test class:
+
+```
+./mvnw verify -Dit.test=Confirm#testBasicPublishAsync
+```
+
 Test reports can be found in `target/failsafe-reports`.
 
 ## Running Against a Broker in a Docker Container
 
 Run the broker:
 
 ```
-docker run -it --rm --name rabbitmq -p 5672:5672 rabbitmq:3.8
+docker run --pull always --rm --tty --interactive --name rabbitmq --publish 5672:5672 rabbitmq:latest
 ```
 
 Launch the tests: