Incorrect code generation for oneOf fields

[nikolaiser]

Describe the bug
Code that is generated for oneOf fields is incorrect

To Reproduce

The following scala-cli script

//> using scala 2.13.12
//> using repository sonatype:snapshots
//> using dep dev.zio::zio-http-gen:3.0.0-RC4+41-2d267b56-SNAPSHOT
//> using dep dev.zio::zio-json-yaml:0.6.2

import zio.http.gen.openapi.EndpointGen
import zio.http.endpoint.openapi.OpenAPI
import zio.http.endpoint.openapi.JsonSchema
import zio.json.yaml._
import zio.schema.codec.JsonCodec
import zio.http.gen.scala.CodeGen
import java.nio.file.Paths

object Main {

  val openapiYaml = """
                      |openapi: 3.0.3
                      |info:
                      | title: Example
                      | description: Example API documentation
                      | version: 1.0.0
                      |paths:
                      | /foo:
                      |   post:
                      |     requestBody:
                      |       content:
                      |         application/json:
                      |           schema:
                      |             $ref: '#/components/schemas/Bar' 
                      |     responses:
                      |       '200':
                      |         description: Success
                      |
                      |components:
                      | schemas:
                      |   Bar:
                      |     type: object
                      |     properties:
                      |       field:
                      |         oneOf:
                      |           - $ref: '#/components/schemas/Baz'
                      |           - $ref: '#/components/schemas/Qux'
                      | 
                      |   Baz:
                      |     type: object
                      |     properties:
                      |       stringField:
                      |         type: string
                      |
                      |   Qux:
                      |     type: object
                      |     properties:
                      |       stringField:
                      |         type: string
  """.stripMargin

  implicit val openapiDecoder = JsonCodec.jsonDecoder(OpenAPI.schema)

  def main(args: Array[String]) = {
    val openapi = openapiYaml.fromYaml[OpenAPI].toOption.get
    val files = EndpointGen.fromOpenAPI(openapi)
    CodeGen.writeFiles(
      files,
      Paths.get("./oneof-output"),
      "foo.bar",
      None
    )
  }
}

Generates a file

package foo.bar.component

import zio.schema._

case class Bar(
 field: Option[Field]
)
object Bar {


 implicit val codec: Schema[Bar] = DeriveSchema.gen[Bar]



}
case class Field(

)
object Field {


 implicit val codec: Schema[Field] = DeriveSchema.gen[Field]



}

Expected behaviour
Fields with a oneOf type should not be represented by an empty case class

[jdegoes]

/bounty $50

[algora-pbc]

💎 $50 bounty created by ZIO
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Attempt	Started (GMT+0)	Solution
🔴 @ekhov	Jan 18, 2024, 6:43:57 PM	WIP
🟢 @987Nabil		#2657

[ekhov]

/attempt #2623

Algora profile	Completed bounties	Tech	Active attempts	Options
@ekhov	1 ZIO bounty + 0 bounties from 0 projects	Python, Scala		Cancel attempt

[ekhov]

Will not finish this in time, everyone is welcome to take this issue

[algora-pbc]

💡 @987Nabil submitted a pull request that claims the bounty. You can visit your bounty board to reward.

[algora-pbc]

🎉🎈 @987Nabil has been awarded $50! 🎈🎊

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