[gen] endpoints with inline response body are missing `zio.schema._` import

[jirihausner]

Describe the bug
When generating endpoints from OpenAPI specification using EndpointGen, zio.schema._ import is missing when using inline response bodies, which breaks the compilation of generated Scala file.

Note: this does not happen for (inline) request bodies.

To Reproduce

//> using scala 3.3.8
//> using dep dev.zio::zio-http-gen:3.11.3

import zio.http.endpoint.openapi.OpenAPI
import zio.http.gen.openapi.{Config, EndpointGen}
import zio.http.gen.scala.CodeGen

object InlineResponseBodyMissingImport extends App {

  val spec: String =
    """|{
       |  "openapi": "3.0.3",
       |  "info": { "title": "Users API", "version": "1.0.0" },
       |  "paths": {
       |    "/user/{id}": {
       |      "get": {
       |        "parameters": [
       |          {
       |            "name": "id",
       |            "in": "path",
       |            "required": true,
       |            "schema": { "type": "string", "format": "uuid" }
       |          }
       |        ],
       |        "responses": {
       |          "200": {
       |            "description": "OK",
       |            "content": {
       |              "application/json": {
       |                "schema": {
       |                  "type": "object",
       |                  "properties": {
       |                    "id":   { "type": "integer" },
       |                    "name": { "type": "string" }
       |                  }
       |                }
       |              }
       |            }
       |          }
       |        }
       |      }
       |    }
       |  }
       |}
       |""".stripMargin
  
  println(spec)

  val openApi: OpenAPI =
    OpenAPI.fromJson(spec).fold(err => sys.error(s"Failed to parse OpenAPI spec: $err"), identity)

  val rendered: Map[String, String] =
    CodeGen.renderedFiles(
      EndpointGen.fromOpenAPI(openApi, Config.default),
      basePackage = "example",
    )

  rendered.foreach { case (path, content) =>
    println(s"=== generated: $path ===")
    println(content)
    println()
  }
}

Got

object Id {

  import zio.http._
  import zio.http.endpoint._
  import zio.http.codec._

  val get = Endpoint(Method.GET / "user" / uuid("id"))
    .in[Unit]
    .out[GET.ResponseBody](status = Status.Ok)

  object GET {

    case class ResponseBody(
      id: Option[Long],
      name: Option[String]
    )
    object ResponseBody {
      implicit val codec: Schema[ResponseBody] = DeriveSchema.gen[ResponseBody]
    }
  }
}

where compilation fails with Not found: type Schema - did you mean Scheme? or perhaps Scheme.type? on implicit val codec: Schema[ResponseBody] = ... line.

Expected behaviour

object Id {

  import zio.http._
  import zio.http.endpoint._
  import zio.http.codec._
  import zio.schema._ // <- this is missing when using inline response bodies

  val get = Endpoint(Method.GET / "user" / uuid("id"))
    .in[Unit]
    .out[GET.ResponseBody](status = Status.Ok)

  object GET {

    case class ResponseBody(
      id: Option[Long],
      name: Option[String]
    )
    object ResponseBody {
      implicit val codec: Schema[ResponseBody] = DeriveSchema.gen[ResponseBody]
    }
  }
}

Root cause

• in zio.http.gen.openapi.EndpointGen, the function private def endpoint(...) which is used to generate endpoint code with imports is ignoring response body imports by returning Nil -> s"$method.${Inline.ResponseBodyType}" unlike request body which includes code.imports