fix(sidecar): [cherry-pick 1.5.1] honor worker namespace suffix (#14955)

[biswapanda]

Summary

• Cherry-picks fix(sidecar): honor worker namespace suffix #14955 (5a6d414575) onto release/1.5.0.
• Makes Rust-side RL publishers compose DYN_NAMESPACE_WORKER_SUFFIX, matching frontend RL discovery and the Python worker path.
• Preserves explicit CLI namespaces and avoids double-appending an existing suffix.

Fixes the namespace-registration asymmetry reported in NVIDIA bug 6731829.

Validation

• cargo fmt --all
• cargo test -p dynamo-backend-common --lib
• cargo test -p dynamo-vllm-sidecar
• cargo clippy -p dynamo-backend-common --all-targets -- -D warnings
• GCP regression validation in nv-prd-dgxc.teleport.sh-dynamo-gcp-dev-02, namespace bis-rl-3 (in progress)

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[github-actions]

👋 Hi biswapanda! Thank you for contributing to ai-dynamo/dynamo.

Just a reminder: The NVIDIA Test Github Validation CI runs an essential subset of the testing framework to quickly catch errors.Your PR reviewers may elect to test the changes comprehensively before approving your changes.

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[biswapanda]

/ok to test 97b25c7

[dagil-nvidia]

Held for Dynamo 1.5.1. release/1.5.0 is closed at RC11, the 1.5.0 GA build, so this cherry-pick must not merge there. Converted to draft; it retargets to release/1.5.1 as soon as that branch is cut (patch targeted for 2026-09-30). Tracked on the Dynamo 1.5.1 cherry-pick canvas.

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[dynamo-ops]

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