CASSJAVA-124: Add GRACEFUL_DISCONNECT support (CEP-59)

[Shanzita]

Summary

Implements client-side support for CEP-59 (Graceful Disconnect – In-Band
Connection Draining) in the Java driver.

When a Cassandra node shuts down, it emits a GRACEFUL_DISCONNECT event to
subscribed connections. The driver:

• Stops sending new requests on the affected connection
• Drains in-flight requests to completion
• Closes the whole pool to the draining node and fails over
• Reconnects automatically via the normal reconnection policy

Design

• Capability is negotiated per connection: every channel that intends to
  register for GRACEFUL_DISCONNECT sends OPTIONS and filters its REGISTER
  against its own SUPPORTED response. There is no driver-global capability
  flag, so mixed-version clusters (rolling upgrades) work correctly.
• The internal GracefulDisconnectEvent is node-scoped: it means "this node
  is shutting down", regardless of whether it arrived on a pool connection or
  the control connection, and the pool drains accordingly.
• If a server advertises the capability but rejects the REGISTER, the driver
  retries once without the event type instead of failing channel init
  (mixed-version / evolving-server tolerance).
• advanced.connection.graceful-disconnect-enabled config option (default true).
• graceful-disconnects (session) and pool.graceful-disconnects (node)
  counters, initialized in the Dropwizard, Micrometer and MicroProfile
  backends and incremented where events are received.

Testing

• 3,552 core unit tests pass (new coverage: ProtocolInitHandler capability
  filtering and REGISTER-rejection degradation, node-scoped ChannelPool drain,
  metric increments, duplicate/late event tolerance)
• New GracefulDisconnectIT: bounded 2-node ccm test that drains a node under
  steady query load and asserts the metric observed the event, queries fail
  over, and zero exceptions reach the application. Gated on Cassandra 7.0+, so
  it is skipped until a server with CEP-59 is available in CI.
• Manually validated end-to-end against a CEP-59 server build
  (CASSANDRA-21191: [CEP-59] Implementation of In-Band Connection Draining (Graceful Disconnect) cassandra#4953) on 2-node and 3-node ccm clusters:
  nodetool drain mid-load → 0 disruptive exceptions, thousands of successful
  queries after the event, drained node goes DOWN cleanly, failover invisible
  to the application. The 3-node run exercised the event arriving on the
  control connection and a pool connection simultaneously.

Depends on: native-protocol 1.5.3-SNAPSHOT (Shanzita/native-protocol:cep-59,
the branch behind datastax/native-protocol#61; installed by install-snapshots.sh
until 1.5.3 is released)
JIRA: CASSJAVA-124