fix: add 30s connection timeout to feed WebSockets

[realfishsam]

Fixes #252
Fixes #253

[realfishsam]

PR Review: VERIFIED

What This Does

Adds a 30-second connection timeout to the establishConnection() method in both BinanceFeed and ChainlinkFeed. If the WebSocket does not emit open, error, or close within 30s, the timeout fires, closes the socket, nulls out state, and rejects the connection promise.

Blast Radius

Two files: core/src/feeds/binance/binance-feed.ts and core/src/feeds/chainlink/chainlink-feed.ts. Changes are structurally identical. Only the establishConnection() method is affected.

Findings

• Timeout is cleared on all three settlement paths (open, close, error). No double-settlement risk.
• ws.close() is used (graceful close) rather than ws.terminate() (hard close). This is appropriate since the connection attempt may have partially completed a TCP handshake.
• The timeout rejects the promise, which will propagate to ensureConnected() -> connect(). Callers should handle this rejection. Looking at both feeds, connect() catches and calls scheduleReconnect(), so the rejection is handled.
• The close handler also clears the timeout. This is correct -- if the connection closes before the timeout fires (e.g., server RST), the timer is cleaned up.
• No settled flag unlike PR fix: opinion fetcher perf + websocket safety #604's Opinion websocket. This is acceptable because ws.close() in the timeout handler will trigger the close event, but by that point the promise is already rejected (the close handler only nulls state and schedules reconnect, it does not resolve/reject). There is no double-rejection risk.

Semver Impact

patch -- bug fix (prevents indefinite hang on feed connection), no API change.

Risk

Low. The pattern is straightforward and mirrors standard WebSocket timeout implementations.