Fix PU plaintext detection when AuthPolicy.NONE is configured

[uuuyuqi]

What is the purpose of the change?

GitHub_issue: #16373

Fixes #16373

This pull request fixes port-unification protocol detection when provider TLS is configured with AuthPolicy.NONE.

AuthPolicy.NONE means TLS is optional. If a client sends a non-TLS first packet to the port-unification port, the server should continue with plaintext protocol detection. The current 3.3 branch enters the TLS-detection branch, sees that the packet is not TLS, and then does nothing when the auth policy is NONE. As a result, plaintext Dubbo detection is skipped and the connection waits until the caller times out.

The fix keeps the existing strict-TLS behavior unchanged:

• TLS first packet: enable SSL and return.
• Non-TLS first packet with required TLS: log, discard data, close the channel, and return.
• Non-TLS first packet with AuthPolicy.NONE: fall through to plaintext detectProtocol(...).

This PR also adds a regression test that provides an optional-TLS test CertProvider, sends a Dubbo plaintext first packet, and verifies that the plaintext protocol detector is invoked.

Verification:

• Before the production fix, the new regression test failed because the detector count was 0 instead of 1.
• mvn -q -pl dubbo-remoting/dubbo-remoting-netty4 -am -Dtest=NettyPortUnificationServerHandlerTest,PortUnificationServerTest,SslServerTlsHandlerTest -Dsurefire.failIfNoSpecifiedTests=false -DskipITs -DskipIntegrationTests=true -Djacoco.skip=true test
• mvn -q -pl dubbo-remoting/dubbo-remoting-netty4 -am -DskipTests -DskipIntegrationTests=true -Djacoco.skip=true -Dcheckstyle.skip=false -Dcheckstyle_unix.skip=false -Drat.skip=false verify
• mvn -q -pl dubbo-remoting/dubbo-remoting-netty4 -am spotless:check

Checklist

• Make sure there is a GitHub_issue field for the change (usually before the description, using GitHub_issue: #123456).
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exists. If the new feature or significant change is added, please remember to add integration-test in dubbo-samples project.
• Make sure gitHub actions can pass, only after CI passed will we review it.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 9.09091% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.86%. Comparing base (316df8e) to head (a4ffa53).
⚠️ Report is 1 commits behind head on 3.3.

Files with missing lines	Patch %	Lines
...port/netty4/NettyPortUnificationServerHandler.java	9.09%	9 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #16374      +/-   ##
============================================
- Coverage     60.87%   60.86%   -0.01%     
+ Complexity    11767    11763       -4     
============================================
  Files          1953     1953              
  Lines         89260    89262       +2     
  Branches      13471    13471              
============================================
- Hits          54334    54333       -1     
+ Misses        29342    29337       -5     
- Partials       5584     5592       +8     

Flag	Coverage Δ
integration-tests-java21	32.09% <9.09%> (+<0.01%)	⬆️
integration-tests-java8	32.19% <9.09%> (-0.02%)	⬇️
samples-tests-java21	32.11% <0.00%> (-0.09%)	⬇️
samples-tests-java8	29.81% <0.00%> (+0.07%)	⬆️
unit-tests-java11	59.14% <9.09%> (+0.04%)	⬆️
unit-tests-java17	58.58% <9.09%> (-0.01%)	⬇️
unit-tests-java21	58.61% <9.09%> (+0.01%)	⬆️
unit-tests-java25	58.54% <9.09%> (+0.02%)	⬆️
unit-tests-java8	59.16% <9.09%> (+0.05%)	⬆️

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[CrazyHZM]

LGTM

[zrlw]

LGTM