fix(ci): use released Java SDK and stabilize integration

[longquanzheng]

Summary

• publish Java SDK 0.0.6 from verified main and update Java examples to that Maven Central release
• remove the Java integration composite build so every Java example test uses released dex-sdk:0.0.6
• recursively encode dataclass fields such as nested datetimes in the Python SDK, ready for its next release
• keep Python examples unchanged until that Python SDK release exists
• compare refreshed Attribute Store schemas by value to remove a pointer-identity race

Validation

• Maven Central dex-sdk:0.0.6 artifact returns HTTP 200
• Java dependency insight resolves io.superdurable:dex-sdk:0.0.6, not a project dependency
• Java examples compile and unit tests pass on JDK 17
• Java examples integration suite passes against released 0.0.6
• Python SDK contracts: 22 passed
• Python 3.11 pre-commit hooks for sdk-python/dex/codec.py
• Server Attribute Store integration suite
• make copyright-check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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