Support shared Behaviors list

[viceroypenguin]

Supports a shared Behaviors list, by applying [Behaviors] to an Attribute, which can then be applied a handler.

[Behaviors(
  typeof(ValidationBehavior<,>), typeof(TransactionBehavior<,>)
)]
public sealed class DefaultBehaviorsAttribute : Attribute;

// usage
[Handler]
[DefaultBehaviors]
internal static partial class AddDataSourceCommand;

Fixes #141

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
...ors/ImmediateHandlersGenerator.TransformHandler.cs	99.09% <100.00%> (+0.04%)	⬆️

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