feat(connectors): add Apache Fluss sink

[adamrecsko]

Which issue does this PR address?

Relates to #3689

Rationale

This is phase 1 of Apache Fluss connector support, enabling Apache Iggy streams to write messages into Fluss.

What changed?

Apache Iggy previously had no sink for writing messages to Apache Fluss. The new sink writes binary, JSON, or text payloads to append-only Fluss log tables, with optional Iggy metadata and
automatic table creation.

Writer buffering, retries, idempotence, SASL authentication, startup validation, and Docker-backed integration tests are included.

Local Execution

• Local checks passed except for full workspace Clippy
• Pre-commit hooks ran and passed
• Passed cargo fmt --all
• Passed cargo sort --check --no-format --workspace
• Passed focused Clippy for iggy_connector_fluss_sink
• Passed all 19 Fluss sink unit tests
• Passed the focused Docker-backed Fluss integration test
• Full workspace Clippy did not pass because of six unrelated existing errors in core/sdk and one in core/server

AI Usage

1. OpenAI Codex.
2. Used for implementation assistance, review remediation, test execution, and PR wording.
3. Verified with formatting, dependency sorting, focused Clippy, unit tests, Docker-backed integration testing, and pre-commit hooks.
4. Yes, I can explain every line of the code if asked.

[github-actions]

Thanks for the PR. It is labeled S-waiting-on-review and queued for review.

Slash commands (own line, regular comment) move it around the queue:

• /ready - back to S-waiting-on-review after addressing feedback
• /author - flip to S-waiting-on-author while you finish changes
• /request-review @user-or-team - request a reviewer

See CONTRIBUTING.md for details.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.74%. Comparing base (01e7210) to head (af17922).
⚠️ Report is 16 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3782      +/-   ##
============================================
- Coverage     75.78%   75.74%   -0.05%     
  Complexity      969      969              
============================================
  Files          1323     1323              
  Lines        159751   159673      -78     
  Branches     133139   133138       -1     
============================================
- Hits         121071   120943     -128     
+ Misses        35045    35026      -19     
- Partials       3635     3704      +69     

Components	Coverage Δ
Rust Core	75.68% <ø> (-0.01%)	⬇️
Java SDK	62.71% <ø> (ø)
C# SDK	71.13% <ø> (-1.16%)	⬇️
Python SDK	93.10% <ø> (ø)
PHP SDK	84.52% <ø> (ø)
Node SDK	96.30% <ø> (+0.15%)	⬆️
Go SDK	43.08% <ø> (ø)
see 34 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[krishvishal]

Thanks for the PR! The CI is failing because Cargo.lock in this branch is internally inconsistent.

This should fix it:

git merge origin/master
cargo check --workspace

[adamrecsko]

Thanks for the PR! The CI is failing because Cargo.lock in this branch is internally inconsistent.

This should fix it:

git merge origin/master
cargo check --workspace

Hi @krishvishal !
Done, sync and rebased onto master and run cargo check --workspace

[adamrecsko]

Small update, I've the moved fluss-rs version management to the workspace dependencies, the source connector does the same, I wanted to be align with that

[krishvishal]

Hey @adamrecsko the CI is failing.Seems its related to fluss version. Please look into it.

Also please rebase with latest master.

You can also join Iggy's discord so we can converse there.

[hubcio]

it might be related to protoc being required, check discussion under #3688

[adamrecsko]

It is most probably the same issue as in the source connector, but I will try to reproduce locally