Ensure PresenceChangedEvent is triggered after presences emission

[7hong13]

What this PR does / why we need it?

It ensures that the PresenceChanged event is posted after the presences flow emission.

Any background context you want to provide?

What are the relevant tickets?

Fixes #

Checklist

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

[codecov]

Codecov Report

Attention: 46 lines in your changes are missing coverage. Please review.

Comparison is base (5989f50) 78.46% compared to head (3f8c591) 79.58%.
Report is 3 commits behind head on main.

Files	Patch %	Lines
...c/main/kotlin/dev/yorkie/document/crdt/CrdtTree.kt	83.33%	4 Missing and 28 partials ⚠️
...ie/src/main/kotlin/dev/yorkie/document/Document.kt	50.00%	5 Missing and 3 partials ⚠️
yorkie/src/main/kotlin/dev/yorkie/core/Client.kt	40.00%	3 Missing ⚠️
...c/main/kotlin/dev/yorkie/document/json/JsonTree.kt	80.00%	2 Missing ⚠️
...orkie/src/main/kotlin/dev/yorkie/util/IndexTree.kt	94.44%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #151      +/-   ##
==========================================
+ Coverage   78.46%   79.58%   +1.11%     
==========================================
  Files          63       63              
  Lines        3743     3845     +102     
  Branches      582      601      +19     
==========================================
+ Hits         2937     3060     +123     
+ Misses        500      463      -37     
- Partials      306      322      +16     

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[skhugh]

I'm not sure if this will be consistent when presences events occur very rapidly.
Maybe we should add test codes to be sure.

[skhugh]

do we need the timeout?

[7hong13]

It is logically unnecessary, but I added it just in case of an unexpected issue which can lead to an indefinite delay in the first() function.
I'll remove it if it looks redundant.

[skhugh]

is it possible for presence events to be changed as below very fast that publishPresenceEvent for publishPresenceEvent is called after it is already unwatched?

Watched -> PresenceChanged -> Unwatched

[7hong13]

I'm not 100% sure that situation will never happen.
I'll fix it to ensure that the PresenceChanged event is ignored when it is already unwatched.

[7hong13]

I'm not sure if this will be consistent when presences events occur very rapidly.
Maybe we should add test codes to be sure.

I haven't checked for rapidly changing presence events, so I'll look into it further and add test codes for it.