Field-level deprecated metadata is dropped for referenced schemas

[ayush22667]

Description

Field-level deprecated and example metadata is omitted when a field's schema
is represented by a $ref. The same metadata is generated correctly for a
primitive field.

This is reproducible with utoipa 5.5.0.

Minimal reproduction

use utoipa::{OpenApi, ToSchema};

#[derive(ToSchema)]
enum CountryAlpha2 {
    US,
    IN,
}

#[derive(ToSchema)]
struct PaymentRequest {
    /// Deprecated: use `profile_id` instead.
    #[schema(deprecated, example = "US")]
    business_country: Option<CountryAlpha2>,

    /// Deprecated: use `profile_id` instead.
    #[schema(deprecated, example = "legacy")]
    business_label: Option<String>,
}

#[derive(OpenApi)]
#[openapi(components(schemas(CountryAlpha2, PaymentRequest)))]
struct ApiDoc;

fn main() {
    let openapi = ApiDoc::openapi();
    let output =
        serde_json::to_string_pretty(&openapi).expect("OpenAPI serialization should succeed");

    println!("{output}");
}

Dependencies:

[dependencies]
serde_json = "1"
utoipa = "5.5.0"

Actual generated schema

{
  "business_country": {
    "oneOf": [
      {
        "type": "null"
      },
      {
        "$ref": "#/components/schemas/CountryAlpha2",
        "description": "Deprecated: use `profile_id` instead."
      }
    ]
  },
  "business_label": {
    "type": [
      "string",
      "null"
    ],
    "description": "Deprecated: use `profile_id` instead.",
    "deprecated": true,
    "example": "legacy"
  }
}

The referenced business_country field keeps its description, but loses:

"deprecated": true,

The primitive business_label field retains both attributes.

The same deprecation omission occurs for a required referenced field, where the
property is emitted directly as a $ref.

Expected behavior

Field-level metadata should be preserved when the field references another
schema. For example:

"business_country": {
  "oneOf": [
    {
      "type": "null"
    },
    {
      "$ref": "#/components/schemas/CountryAlpha2"
    }
  ],
  "description": "Deprecated: use `profile_id` instead.",
  "deprecated": true,
  "example": "US"
}

Additional context

This appears related to the composite-schema limitation discussed in #1394,
where OneOfBuilder does not support deprecation metadata. However, this report
is specifically about metadata silently being dropped from a field whose type
is a referenced schema.

The behavior was also observed with utoipa 4.2.3, where optional references
are represented using nullable allOf.

[hiSandog]

I would make the reported environment part of the regression coverage for Field-level deprecated metadata is dropped for referenced schemas, rather than leaving it as a manual reproduction. That is especially helpful if future dependency or toolchain updates touch deprecated.