feat(abstractions): deprecate [Event] attribute in favor of [FromEvent]

[j-d-ha]

Summary

Deprecate the [Event] attribute in favor of a new [FromEvent] attribute to align with ASP.NET Core conventions like [FromBody], [FromQuery], [FromRoute], etc.

Motivation

• Convention alignment: ASP.NET Core uses [From*] naming pattern for parameter binding attributes
• Clarity: The [From*] pattern makes it explicit where the parameter value comes from
• Consistency: Developers familiar with ASP.NET Core will recognize the pattern immediately

Tasks

• Create new [FromEvent] attribute with same functionality as [Event]
• Mark [Event] attribute as [Obsolete] with appropriate warning message
• Update documentation to recommend [FromEvent]
• Add migration guide in documentation
• Update all examples and samples to use [FromEvent]
• Add tests for [FromEvent] attribute
• Plan deprecation timeline (consider removing in next major version)

Migration Example

// Old (deprecated)
public class MyHandler
{
    public string Handle([Event] MyEvent evt) => evt.Message;
}

// New (recommended)
public class MyHandler
{
    public string Handle([FromEvent] MyEvent evt) => evt.Message;
}

Breaking Change Considerations

This change should be introduced as non-breaking:

• Keep [Event] working alongside [FromEvent]
• Mark as obsolete with compiler warning
• Remove in next major version (v2.0.0 or later)