Add max-connection-age support for Triple server (connection rotation for load balancing)

[digyear]

What is the purpose of the change

Add server-side max-connection-age support for the Triple protocol, aligned with the standard gRPC capability (gRFC A9: Server-Side Connection Management).

HTTP/2 multiplexes all requests over a single long-lived connection, so a Triple consumer stays pinned to the same provider instance forever — even after new instances are scaled up or traffic should be rebalanced. gRPC solves this with maxConnectionAge / maxConnectionAgeGrace: when a connection exceeds the configured age, the server sends an advisory GOAWAY (NO_ERROR, last-stream-id = MAX_INT) so in-flight requests keep running while clients migrate to a new connection (and get redistributed by the load balancer), then closes the connection after the grace period.

Triple currently has no equivalent: there is no way for a Triple server to proactively rotate long-lived connections. This PR adds it, disabled by default.

Brief changelog

• TripleConfig: add maxConnectionAge (ms, default -1 = disabled) and maxConnectionAgeGrace (ms, default 10000) with validation, following the existing field conventions (getXxxOrDefault()); matching TripleBuilder methods in dubbo-config-api.
• TripleServerConnectionHandler: on channelActive, if maxConnectionAge > 0, schedule a one-shot task on the channel's EventLoop with ±10% jitter (same as grpc-java) to avoid mass simultaneous reconnections when many connections are established at the same time. On expiry:
  1. send the advisory GOAWAY via the existing GracefulShutdown.sendGoAwayFrame (reuses the production code path — in-flight streams are unaffected);
  2. after the grace period, initiate close through ctx.channel().close() so the request traverses this handler's close() override and runs the existing graceful-shutdown sequence (final GOAWAY + PING) instead of an abrupt disconnect;
  3. pending tasks are cancelled on channelInactive (no leaks when the client disconnects first).
• TripleHttp2Protocol: pass the config into the handler on both server pipeline paths (direct h2 and h1-upgrade); raise the codec's gracefulShutdownTimeoutMillis to at least the configured grace so Netty's built-in backstop never fires before it.

Usage:

dubbo:
  protocol:
    name: tri
    triple:
      max-connection-age: 3600000      # rotate connections after ~1h
      max-connection-age-grace: 10000  # let in-flight requests finish

Verifying this change

New tests (all passing):

• TripleServerConnectionHandlerTest — EmbeddedChannel with virtual clock: advisory GOAWAY (NO_ERROR + extraStreamIds=MAX_INT) fires within the jitter window and never before it; disabled by default (24h, no frames); tasks cancelled on channelInactive; graceful-shutdown sequence (final GOAWAY + PING) initiated after the grace period.
• TripleServerConnectionHandlerConcurrencyTest — real NIO server/client, 100 connections sharing 2 EventLoop threads: concurrent rotation of all connections; client disconnects racing age expiry (random delays within ±20% of the window); server-side close() racing pending age tasks; 5 rounds of connection churn under ResourceLeakDetector.PARANOID with zero leak reports.
• TripleConfigTest / TripleBuilderTest — defaults, validation and builder wiring.

Regression: full test suites of dubbo-rpc-triple (492), dubbo-common (1169) and dubbo-config-api (695) pass locally.

Note for reviewers: with the current consumer-side GOAWAY handling (#16344), each rotation costs one request failure window on the consumer, so this feature is best paired with the graceful consumer migration in #16345. This PR is independent and safe to merge on its own (default: disabled).

Does this pull request potentially affect one of the following parts

• Dependencies (does it add or upgrade a dependency)
• The public API (new optional TripleConfig fields; default values keep behavior unchanged)
• The persistence format of the configurations
• The default values of configurations (new fields only; existing defaults untouched)
• The serialization protocol
• The compatibility with previous versions

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? JavaDoc on the new TripleConfig fields (website docs can follow after merge)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.65079% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.94%. Comparing base (dab47b7) to head (d88fc01).

Files with missing lines	Patch %	Lines
...he/dubbo/rpc/protocol/tri/TripleHttp2Protocol.java	66.66%	2 Missing ⚠️
...l/tri/transport/TripleServerConnectionHandler.java	94.59%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #16454      +/-   ##
============================================
+ Coverage     60.91%   60.94%   +0.02%     
- Complexity       15    11768   +11753     
============================================
  Files          1953     1953              
  Lines         89271    89331      +60     
  Branches      13473    13479       +6     
============================================
+ Hits          54383    54440      +57     
+ Misses        29309    29306       -3     
- Partials       5579     5585       +6     

Flag	Coverage Δ
integration-tests-java21	32.07% <19.04%> (-0.06%)	⬇️
integration-tests-java8	32.19% <19.04%> (-0.02%)	⬇️
samples-tests-java21	32.11% <3.17%> (-0.06%)	⬇️
samples-tests-java8	29.71% <3.17%> (-0.13%)	⬇️
unit-tests-java11	59.21% <93.65%> (+0.04%)	⬆️
unit-tests-java17	58.67% <93.65%> (+0.02%)	⬆️
unit-tests-java21	58.67% <93.65%> (+0.02%)	⬆️
unit-tests-java25	58.64% <93.65%> (+0.04%)	⬆️
unit-tests-java8	59.20% <93.65%> (+0.02%)	⬆️

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