feat(java): add TCP/TLS integration tests and examples

[atharvalade]

Which issue does this PR close?

Closes #2805

Rationale

The Java SDK had TLS builder methods but no integration tests connecting to a TLS server and no TLS examples.

What changed?

Existing tests only verified TLS builder method chaining but never actually connected to a TLS server.

Added TlsConnectionTest integration test using Testcontainers with TLS certificates mounted from core/certs/. Tests cover: TLS connection with CA cert, TLS connection with server cert, plain TCP failure when TLS is required, and full send/receive message flow over TLS. Added TcpTlsProducer and TcpTlsConsumer examples using IggyTcpClient.builder().enableTls().tlsCertificate(...).

Local Execution

Passed. spotlessCheck and compileJava/compileTestJava clean in both examples/java and foreign/java.

AI Usage

1. Opus 4.6
2. guided by existing GettingStarted examples, BaseIntegrationTest, and C# TLS test patterns
3. Compiled and linted locally, verified code follows existing patterns exactly
4. Yes

[atharvalade]

Resolved

[mmodzelewski]

WIP

It's best if you mark WIP PRs as drafts — that way it's clearly visible from the list that they're not pending maintainer action.

[atharvalade]

WIP

It's best if you mark WIP PRs as drafts — that way it's clearly visible from the list that they're not pending maintainer action.

Will keep that in mind. Though these issues aren't WIP anymore. I'll update the comments.

[mmodzelewski]

Cheers @atharvalade. I'll have a proper look at this later. Just a quick note - could you include these examples in the README? They're picked up by the run-java-examples-from-readme.sh script in the CI. Unless they're actually executed as part of the build, they’ll likely become outdated quite fast.