Add appropriate guards to websocket actions

[bachya]

Describe what the PR does:

From looking at Home Assistant logs, it's apparent that the SimpliSafe websocket, like the REST API, is a little flaky. This leads the current websocket implementation to connect/disconnect too many times, trigger the watchdog spuriously, etc. So, this PR adds some guards:

1. async_connect only attempts to connect if we aren't already connected.
2. Same with async_disconnect.
3. We only trigger the watchdog if its underlying task hasn't already been cancelled.

Does this fix a specific issue?

Fixes https://github.com/bachya/python-simplisafe/issues/

Checklist:

• Confirm that one or more new tests are written for the new functionality.
• Run tests and ensure everything passes (with 100% test coverage).
• Update README.md and docs/ with any new documentation.
• Add yourself to AUTHORS.md.

[qlty-cloud-legacy]

Code Climate has analyzed commit e48e8e3 and detected 0 issues on this pull request.

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[codecov]

Codecov Report

Merging #292 (e48e8e3) into dev (2f92156) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #292   +/-   ##
=======================================
  Coverage   99.77%   99.77%           
=======================================
  Files          13       13           
  Lines         900      903    +3     
=======================================
+ Hits          898      901    +3     
  Misses          2        2           

Impacted Files	Coverage Δ
simplipy/websocket.py	100.00% <100.00%> (ø)

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