feat(types): add responseTime parameter to customErrorMessage

[MarcusHong]

Description

Add responseTime parameter to customErrorMessage type definition to allow access to the request's response time when creating custom error messages.

Changes

• Updated TypeScript type definition for customErrorMessage to include responseTime parameter
• Response time is provided in milliseconds, consistent with pino-http's existing timing

Example Usage

const logger = pinoHttp({
  customErrorMessage: (req, res, err, responseTime) => {
    return `${err.message} (took ${responseTime}ms)`;
  }
});

[mcollina]

Thanks for opening a PR! Can you please add a unit test? We use tsd for the types