CAMEL-23431: Migrate AS2 tests from AvailablePortFinder to port-0 binding

[gnodet]

CAMEL-23431

Summary

Migrate AS2 test infrastructure from AvailablePortFinder to direct port-0 ServerSocket binding to eliminate the TOCTOU (time-of-check-to-time-of-use) race condition that causes flaky BindException failures in CI.

Production code changes:

• Add getLocalPort() to AS2ServerConnection and AS2AsyncMDNServerConnection to expose the OS-assigned port after binding

Test changes (10 files):

• AS2MessageTestBase, AS2MessageTest, AS2UnencryptedMessageTest: API tests now create servers with port 0 and read back the actual port
• AS2AsyncMDNServerConnectionTest: Uses port 0 directly
• AS2ServerManagerITBase, AS2ServerManagerIT, AS2ServerManagerEncryptedIT: Component tests use port 0 in configuration, read back actual port via doPostSetup()
• AS2ServerSecTestBase: Same pattern for security test base class

Not migrated yet (follow-up):

• 8 component tests that create their own "partner" servers require lifecycle restructuring (the port must be known before the Camel context starts). These still use AvailablePortFinder.find() with @RegisterExtension.

Test plan

• mvn test in camel-as2-api — 94 tests pass
• mvn test in camel-as2-component — 12 tests pass
• CI green

[github-actions]

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[github-actions]

🧪 CI tested the following changed modules:

• components/camel-as2/camel-as2-api
• components/camel-as2/camel-as2-component

All tested modules (9 modules)

• Camel :: AS2 :: API
• Camel :: AS2 :: Component
• Camel :: JBang :: MCP
• Camel :: JBang :: Plugin :: Route Parser
• Camel :: JBang :: Plugin :: TUI
• Camel :: JBang :: Plugin :: Validate
• Camel :: Launcher :: Container
• Camel :: YAML DSL :: Validator
• Camel :: YAML DSL :: Validator Maven Plugin

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