Fix potential deadlock

[martincostello]

• Fix a potential deadlock where the server never stops by checking the result of WaitToReadAsync() and by passing the CancellationToken to ReadAsync().
• Give the server as long as it needs to start in tests/examples, then cancel after started.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 97.56%. Comparing base (68ae617) to head (4647513).

Files	Patch %	Lines
src/AwsLambdaTestServer/RuntimeHandler.cs	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #668   +/-   ##
=======================================
  Coverage   97.56%   97.56%           
=======================================
  Files           8        8           
  Lines         287      288    +1     
  Branches       30       31    +1     
=======================================
+ Hits          280      281    +1     
+ Misses          3        2    -1     
- Partials        4        5    +1     

Flag	Coverage Δ
linux	96.87% <33.33%> (-0.69%)	⬇️
macos	96.87% <33.33%> (+0.01%)	⬆️
windows	97.56% <33.33%> (+<0.01%)	⬆️

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