Fix LiveQuery reconnection bug

[cbaker6]

Provides a number of essential fixes and updates to ParseLiveQuery:

• Add sendPing and sendPingPublisher for LiveQuery web socket connections
• Add openPublisher for LiveQuery
• Fix bug where a web socket task was being reused after it was closed resulting in the inability to reconnect
• Improve LiveQuery by closing the respective web socket connection when no more subscriptions exist
• Improve error handling in LiveQuery
• Improve not throwing an error when having multiple subscriptions and only unsubscribing from one
• Add testcases
• Update playground examples
• Add changelog entry

[codecov]

Codecov Report

Merging #172 (068525c) into main (f877b37) will decrease coverage by 0.10%.
The diff coverage is 83.33%.

❗ Current head 068525c differs from pull request most recent head 221944e. Consider uploading reports for the commit 221944e to get more accurate results

@@            Coverage Diff             @@
##             main     #172      +/-   ##
==========================================
- Coverage   82.20%   82.09%   -0.11%     
==========================================
  Files          70       71       +1     
  Lines        6596     6641      +45     
==========================================
+ Hits         5422     5452      +30     
- Misses       1174     1189      +15     

Impacted Files	Coverage Δ
...t/LiveQuery/Protocols/ParseLiveQueryDelegate.swift	20.00% <ø> (+20.00%)	⬆️
Sources/ParseSwift/LiveQuery/LiveQuerySocket.swift	62.90% <40.00%> (+1.49%)	⬆️
.../ParseSwift/LiveQuery/ParseLiveQuery+combine.swift	71.42% <71.42%> (ø)
Sources/ParseSwift/LiveQuery/ParseLiveQuery.swift	76.03% <92.68%> (+1.62%)	⬆️
Sources/ParseSwift/Internal/Data+hexString.swift	68.96% <0.00%> (-31.04%)	⬇️
Sources/ParseSwift/Coding/AnyEncodable.swift	61.18% <0.00%> (-0.66%)	⬇️
Sources/ParseSwift/Objects/ParseObject.swift	77.27% <0.00%> (-0.27%)	⬇️
Sources/ParseSwift/Types/Query.swift	93.20% <0.00%> (-0.18%)	⬇️
... and 3 more

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[cbaker6]

@TomWFox can you kindly look through the added docs?