feature request: Add support for int enums

[ghostbuster91]

Motivation

When translating from OpenAPI to Smithy, schemas that define enums with an integer type (e.g. type: integer + enum: [...]) are currently mapped to plain enum in Smithy which is incorrect.

Expected behavior

Given an OpenAPI schema like:

Status:
  type: integer
  enum: [0, 1, 2]
  x-enum-varnames:
    - PENDING
    - ACTIVE
    - ARCHIVED

The generated Smithy model should be:

intEnum Status {
  PENDING  = 0
  ACTIVE   = 1
  ARCHIVED = 2
}

Current behavior

The same schema is currently translated into:

enum Status {
  PENDING
  ACTIVE
  ARCHIVED
}

Why x-enum-varnames?

OpenAPI itself does not support named integer enums directly.

The common convention (used by OpenAPI Generator, Swagger Codegen, etc.) is to combine:

type: integer
enum: [...]
x-enum-varnames: [...] (vendor extension to preserve symbolic names)

This provides both wire values (integers) and stable names for code generation.