Clean up methods related to presence

[chacha912]

What this PR does / why we need it?

This is a follow-up task of #574

• Add presence to unwatched event
  • We can use it in examples: Add simultaneous cursors example and Update examples to v0.4.6 #581
• Return presence to user by retrieving only online clients and making a copy

Any background context you want to provide?

When detaching, there are two possible scenarios:

When UserA detaches, a change is made to remove the presence, and the watch stream is canceled.

1. If UserB receives the unwatched event first, UserB will remove UserA from onlineClients and trigger the unwatched event.

2. If UserB receives the pushpull response first, which includes a change to remove presence, UserB will trigger the unwatched event beforehand while detaching since it involves unwatching.

What are the relevant tickets?

Fixes #

Checklist

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #599 (b2eb6d4) into main (1decb55) will decrease coverage by 0.38%.
The diff coverage is 96.42%.

@@            Coverage Diff             @@
##             main     #599      +/-   ##
==========================================
- Coverage   87.52%   87.15%   -0.38%     
==========================================
  Files          81       81              
  Lines        7953     8048      +95     
  Branches      816      818       +2     
==========================================
+ Hits         6961     7014      +53     
- Misses        679      720      +41     
- Partials      313      314       +1     

Files Changed	Coverage Δ
src/client/client.ts	75.17% <66.66%> (-1.92%)	⬇️
src/document/document.ts	76.27% <90.00%> (+0.78%)	⬆️
test/integration/presence_test.ts	88.93% <97.93%> (-11.07%)	⬇️
test/helper/helper.ts	67.92% <100.00%> (-13.71%)	⬇️
test/integration/client_test.ts	99.65% <100.00%> (ø)
test/integration/document_test.ts	98.98% <100.00%> (ø)

[hackerwins]

Thanks for your contribution. 👍

[hackerwins]

LGTM. 👍

Dealing with asynchronous events used to be challenging, but it seems that presence and document.subscribe events are now stable.

However, there are still some non-deterministic behaviors in our test cases. We need to address them to be deterministic in the next tasks.