Fix Concurrency issues with StateChange hooks and add/removing channels

[dsrees]

There are still a few ConcurrentModificationExceptions occurring. These are caused by clients adding a callback hook inside of a callback hook or modifying the channels while handling an error, etc.

the solution is to make lists as read-only and then whenever adding or removing hooks and channels, use only concurrently safe operations by converting the read-only list to a new mutable list, adding the value, and then returning the new list.

This allows for looping over an existing list and adding a value to that list at the same time without modifying the underlying list while it's being looped over.

[dsrees]

@AdamGrzybkowski

[codecov-io]

Codecov Report

Merging #70 into master will increase coverage by 0.06%.
The diff coverage is 95.83%.

@@             Coverage Diff              @@
##             master      #70      +/-   ##
============================================
+ Coverage     91.36%   91.43%   +0.06%     
  Complexity      178      178              
============================================
  Files             9        9              
  Lines           533      537       +4     
  Branches         72       71       -1     
============================================
+ Hits            487      491       +4     
+ Misses           13       12       -1     
- Partials         33       34       +1

Impacted Files	Coverage Δ	Complexity Δ
src/main/kotlin/org/phoenixframework/Socket.kt	92.35% <100%> (-0.33%)	71 <5> (ø)
src/main/kotlin/org/phoenixframework/Push.kt	83.33% <50%> (-0.67%)	25 <0> (ø)
.../main/kotlin/org/phoenixframework/DispatchQueue.kt	66.66% <0%> (+11.11%)	0% <0%> (ø)	⬇️

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[AdamGrzybkowski]

@dsrees I don't think this extension copyAndAdd is needed

converting the read-only list to a new mutable list, adding the value, and then returning the new list

this could be achieved with kotlin plus operator. I've left a comment in the commit to master.