refactor: simplify connection establishment

[arthurschreiber]

• Instead of calling this.socketError, throw errors and have them handled centrally in initialiseConnection.
• Use async/await wherever possible.

[codecov]

Codecov Report

Attention: Patch coverage is 76.05634% with 51 lines in your changes missing coverage. Please review.

Project coverage is 86.09%. Comparing base (e1b37fb) to head (8fc86dc).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/connection.ts	76.05%	49 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1663      +/-   ##
==========================================
+ Coverage   85.47%   86.09%   +0.62%     
==========================================
  Files          90       90              
  Lines        4859     4853       -6     
  Branches      924      920       -4     
==========================================
+ Hits         4153     4178      +25     
+ Misses        702      670      -32     
- Partials        4        5       +1     

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