Make async service call use awaitable, session open improvements

[mregen]

Proposed changes

• Improvements when many sessions need to be opened
• Introduce a OpenAsync version which usesmore async calls for session creation
• add async interfaces to cert validator
• refactor lock of encodeable factory
• add a EndAsync property to WriteRequest to allow to await a service call
• add a EndSendRequestAsync method to allow implementation of awaitable service calls

Related Issues

• Fixes #

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Test enhancement (non-breaking change to increase test coverage)
• Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• Documentation Update (if none of the other choices apply)

Checklist

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• I ran tests locally with my changes, all passed.
• I fixed all failing tests in the CI pipelines.
• I fixed all introduced issues with CodeQL and LGTM.
• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
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Further comments

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[codecov]

Codecov Report

Patch coverage: 68.54% and project coverage change: -0.06% ⚠️

Comparison is base (229b124) 59.07% compared to head (ec20ed1) 59.01%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2318      +/-   ##
==========================================
- Coverage   59.07%   59.01%   -0.06%     
==========================================
  Files         330      330              
  Lines       63331    63646     +315     
==========================================
+ Hits        37413    37561     +148     
- Misses      25918    26085     +167     

Files Changed	Coverage Δ
Libraries/Opc.Ua.Client/NodeCache.cs	70.04% <0.00%> (-1.42%)	⬇️
Libraries/Opc.Ua.Client/TraceableSession.cs	49.39% <0.00%> (-1.05%)	⬇️
...indings.Https/Stack/Https/HttpsTransportChannel.cs	77.38% <0.00%> (-0.40%)	⬇️
Stack/Opc.Ua.Core/Stack/Client/UaChannelBase.cs	21.24% <0.00%> (-0.34%)	⬇️
...k/Opc.Ua.Core/Stack/Tcp/UaSCBinaryClientChannel.cs	62.87% <48.83%> (-2.02%)	⬇️
Libraries/Opc.Ua.Client/Session.cs	68.53% <51.70%> (-1.71%)	⬇️
...ack/Opc.Ua.Core/Stack/Tcp/ChannelAsyncOperation.cs	63.43% <61.53%> (-1.52%)	⬇️
...ck/Opc.Ua.Core/Types/Encoders/EncodeableFactory.cs	68.38% <68.65%> (-4.55%)	⬇️
...pc.Ua.Core/Stack/Tcp/UaSCBinaryTransportChannel.cs	87.60% <83.33%> (-0.33%)	⬇️
...Core/Security/Certificates/CertificateValidator.cs	80.08% <85.50%> (-0.66%)	⬇️
... and 3 more

... and 15 files with indirect coverage changes

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