test: expand websocket connection and payload parser coverage

[musfaagv]

Motivation

• Improve test coverage and reliability for WebSocket-related UI and connection logic to prevent regressions when switching data sources and handling JSON WS payloads.
• Verify the Connect modal exposes the WebSocket tab and that the connect flow uses the URL input as expected.
• Ensure the WebSocket payload parser maps ultrasonic payloads to chart data safely and doesn't crash on invalid input.

Description

• Updated src/components/__tests__/ConnectModal.test.tsx to explicitly assert the WebSocket tab is present/selectable, verify the WebSocket URL input default value, and confirm the onConnectWebSocket callback is invoked with the updated URL.
• Rewrote src/hooks/__tests__/useDataConnection.test.ts to mock useWebSocket (and useSerial/generator) with deterministic state and spies, and added transition tests for generator -> websocket, serial -> websocket, disconnect, plus write() behavior (successful when websocket-connected, throws when disconnected).
• Extended src/utils/__tests__/wsPayload.test.ts to assert valid ultrasonic JSON maps to chart values [cm, inch] and to assert invalid payloads are handled safely (no crash and return null).

Testing

• Ran the targeted test suite with npm test -- src/components/__tests__/ConnectModal.test.tsx src/hooks/__tests__/useDataConnection.test.ts src/utils/__tests__/wsPayload.test.ts.
• All targeted tests passed: 3 test files executed and 11 tests passed (no failures).

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Codex Task