fix: use ConfigureAwait(false) on all awaits

[gnjack]

Description

Use ConfigureAwait(false) on all awaits. This was already present on some awaits in KafkaFlow, but applied inconsistently.

This allows awaits to continue without forcing the callback to be invoked on the original context or scheduler. This can improve performance and help prevent deadlocks when used in environments with a SynchronizationContext such as ASP .NET Framework or UI applications.

This seems to be best practice in libraries (even if it unfortunately makes async code less simple / clean):

• https://devblogs.microsoft.com/dotnet/configureawait-faq/
• https://blog.stephencleary.com/2017/03/aspnetcore-synchronization-context.html
• https://blog.stephencleary.com/2023/11/configureawait-in-net-8.html

Fixes #563

How Has This Been Tested?

We stopped experiencing stalls in Kafka message consumption in ASP .NET Framework after making this change.

All unit / integration tests pass.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests to cover my changes
• I have made corresponding changes to the documentation

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[gnjack]

The Roslyn analyzer rule CA2007 can detect this to help prevent new awaits being added without ConfigureAwait(false) but it looks like those aren't enabled - we'd need to explicitly EnableNETAnalyzers in the .NET standard projects.

It also looks like are using Codacy / SonarCube which has rule S3216 to pick this up, but I'm not sure if it'll correctly fire for .NET Standard projects.