fix(core): stop polling timers on restart and disconnect - #363

Summary

• Stop the controller-owned polling timer when startPolling() is called again, when stopPolling() is called, and when the host disconnects.
• Document the timer lifecycle and add a patch changeset.

Related to the historical disconnect-polling report in #192. That report's reproduction used the pollInterval option; this change covers the separate manual startPolling() interval, which survives host disconnection after the controller cleanup refactor.

Validation

• npm exec -- tsc --noEmit --pretty false -p packages/core/tsconfig.json — passed.
• ESLint on both changed TypeScript files — no errors; one existing deprecation warning at apollo-query-controller.ts:389.
• Synthetic probe against the bundled controller source verified timer replacement, explicit stop, and host-disconnect cleanup.
• The targeted Web Test Runner invocation could not import the test module on native Windows (Failed to resolve module specifier "\ttestschema.ts"), so that browser test did not execute. No full-suite or CI result is claimed.