feat(microservices): add event typings to the @EventPattern decorator

[joelday]

Adds overloads for @EventPattern to allow validation that decorated method signatures match event payload types based on a specified mapping type. Includes tests demonstrating correct usage and error cases with // @ts-expect-error.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Adds overloads to the @EventPattern decorator that creates a static type constraint between the pattern and the decorated method's parameter type.

Example:

type FooMessage = {
  foo: string;
};

type BarMessage = {
  bar: number;
};

type EventTypes = {
  'event-pattern-foo': FooMessage;
  'event-pattern-bar': BarMessage;
};

class FooBarTestComponent {
  // correct
  @EventPattern<EventTypes>('event-pattern-bar')
  testBar(event: BarMessage) {}

  // incorrect (foo is specified, but the parameter type is `string` instead of `FooMessage`
  @EventPattern<EventTypes>('event-pattern-foo')
  testFoo(event: string) {}
}

Does this PR introduce a breaking change?

• Yes
• No

Other information

• I'm unsure of what documentation should be added/where that lives.
• I'm unsure of whether or not topic is an appropriate name for these overloads instead of metadata.

[coveralls]

Pull Request Test Coverage Report for Build 17672a4a-de8d-4a97-8fa2-abef07e8be32

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.292%

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Totals
Change from base Build 4f1bfe2a-3a8e-4431-8410-1516cf911760:	0.0%
Covered Lines:	7146
Relevant Lines:	8003

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💛 - Coveralls

Pull Request Overview

This PR adds static type overloads for the @EventPattern decorator to ensure the decorated method's parameter types align with the event payload types specified in a mapping type, along with tests to verify the desired behavior.

• Introduces generic, typed overloads for @EventPattern in the decorator file
• Adds type safety tests in the corresponding spec file to demonstrate correct usage and expected error conditions

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/microservices/test/decorators/event-pattern.decorator.spec.ts	Adds new static type safety tests for the @EventPattern decorator overloads
packages/microservices/decorators/event-pattern.decorator.ts	Introduces typed overloads for the EventPattern decorator to enforce correct event payload types

Comments suppressed due to low confidence (1)

packages/microservices/decorators/event-pattern.decorator.ts:33

• [nitpick] Consider aligning the parameter naming between the typed overloads (using 'topic') and the untyped overloads (using 'metadata') for improved consistency and clarity. This may help reduce confusion about the intended usage.

<TEventTypes extends Record<string, any>>(