Prevent simultaneous connections

[Gold872]

Previously, if the IP address was changed while network tables was disconnected, there would be a new connection attempt "loop" that tried to connect at the same time as the existing connection attempt "loop(s)". When the connection was eventually established, multiple clients would be created on Network Tables.

Now, when trying to connect, any additional calls to _connect() while trying to connect will be blocked off, preventing this issue

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 75.91%. Comparing base (9dcd004) to head (f5155ef).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
lib/services/nt4_client.dart	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #202      +/-   ##
==========================================
- Coverage   75.92%   75.91%   -0.02%     
==========================================
  Files          79       79              
  Lines        8624     8626       +2     
==========================================
  Hits         6548     6548              
- Misses       2076     2078       +2     

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