feat(check): add chunk-stream check

[martinconic]

Adds a chunk-stream check exercising bee's new /chunks/stream download mode (ethersphere/bee#TBD), plus the websocket client it needs.

What it does

Streams chunks up to one node over a single websocket, then streams them back from a different node over another, asserting the guarantee that matters: exactly one delivery per requested address, matched by address rather than arrival order, no duplicates, no unrequested deliveries, and byte-for-byte identical data.

It also asserts that an address never uploaded comes back as 0x01 not-found — which exercises retrieval exhausting every peer, a path unit tests can't reach.

Changes

• pkg/bee/api/chunkstream.go — ChunkStreamService on the API client. Upload and download streams, ChunkDelivery{Status, Address, Data}, exported status constants. Derives ws/wss from the client's scheme rather than hardcoding ws:// as pkg/wslistener does, and fails the handshake if the node doesn't echo the negotiated subprotocol — which alone catches a node without the feature.
• pkg/check/chunkstream/ — the check and its metrics, modelled on retrieval.
• Registered as chunk-stream; config in config.yaml and local.yaml (ci-chunk-stream).