fix(core) #1239

[R11baka]

fix #1239
TLDR added type for handler method

[willfarrell]

Thanks for the PR. Would you be able to update the TS tests so that they pass? Once passing I can merge this into the v6 branch which is set to release later this month.

packages/core/index.test-d.ts:411:0
  ✖  411:0   Parameter type MiddyfiedHandler<S3Event, any, Error, Context, {}> is not identical to argument type MiddyfiedHandler<S3Event, void, Error, Context, {}>.                                                                                                                                                                                                                                                                                                                    
  ✖  415:18  Parameter event implicitly has an any type.                                                                                                                                                                                                                                                                                                                                                                                                                                 
  ✖  4[18](https://github.com/middyjs/middy/actions/runs/11817380388/job/32924868218?pr=1257#step:5:19):0   Parameter type MiddyfiedHandler<APIGatewayProxyEvent, number, Error, Context, {}> is not identical to argument type MiddyfiedHandler<any, number, Error, Context, {}>.                                                                                                                                                                                                                                                                                                      
  ✖  422:2   Unused @ts-expect-error directive.                                                                                                                                                                                                                                                                                                                                                                                                                                          
  ✖  426:65  Argument of type MiddyfiedHandler<APIGatewayProxyEvent, string, Error, Context, {}> is not assignable to parameter of type MiddyfiedHandler<APIGatewayProxyEvent, number, Error, Context, {}>.
  Types of property before are incompatible.
    Type AttachMiddlewareFn<APIGatewayProxyEvent, string, Error, Context, {}> is not assignable to type AttachMiddlewareFn<APIGatewayProxyEvent, number, Error, Context, {}>.
      Type string is not assignable to type number.  

  5 errors