Reduce locking in secure channel client send/receive codepath

[mregen]

Proposed changes

During high load there were a few portions in the send/receive pipeline identified which may cause lock contention and thread starvation due to locks:

• Remove lock for the codepath when a incoming message is processed.
• Add a concurrent dictionary to allow for the processing of OperationCompleted and to add new requests without locking
• Allow to process normal service requests without locking

Due to the change it is possible to send KeepAlive even when a incoming message is received.

Related Issues

• Fixes #

Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply. You can also fill these out after creating the PR.

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] 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

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [ ] I have read the CONTRIBUTING doc.
• [ ] I have signed the CLA.
• [ ] 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.
• [ ] I have added necessary documentation (if appropriate).
• [ ] Any dependent changes have been merged and published in downstream modules.

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 62.50000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 53.98%. Comparing base (22096f4) to head (85da87f).

Files	Patch %	Lines
Stack/Opc.Ua.Core/Stack/Tcp/UaSCBinaryChannel.cs	33.33%	4 Missing :warning:
...k/Opc.Ua.Core/Stack/Tcp/UaSCBinaryClientChannel.cs	80.00%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2531 +/- ## ========================================== + Coverage 53.97% 53.98% +0.01% ========================================== Files 335 335 Lines 64526 64524 -2 Branches 13267 13268 +1 ========================================== + Hits 34826 34832 +6 + Misses 25939 25932 -7 + Partials 3761 3760 -1 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[mregen]

found an issue due to new exceptions -- investigating