fix: Add heartbeat callback; Move to Sets vs Arrays

[filipecabaco]

What kind of change does this PR introduce?

Add heartbeat callback; Move to Sets vs Arrays

[Copilot]

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull Request Overview

This PR introduces a heartbeat callback mechanism and refactors channel storage from arrays to Sets within the RealtimeClient, along with updating the tests accordingly.

• Updates test assertions to use the new getChannels() helper instead of directly accessing the channels property.
• Implements heartbeat callback functionality with additional tests for both successful and error heartbeats.
• Refactors channel creation and removal logic to work with a Set instead of an array.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
test/client.test.ts	Updated test assertions to retrieve channels via getChannels() and added heartbeat tests.
test/channel.test.ts	Updated channel removal assertions to use getChannels().
src/RealtimeClient.ts	Changed channels from an array to a Set; added HeartbeatStatus type and heartbeat callback methods; updated channel creation and removal logic.

Comments suppressed due to low confidence (1)

src/RealtimeClient.ts:426

• There is a spelling mistake in the error message ('hearbeat timeout'). It should be corrected to 'heartbeat timeout'.

this.conn?.close(WS_CLOSE_NORMAL, 'hearbeat timeout')