feat: add type definitions

[George-Payne]

Adds typescript types.

[github-actions]

🎉 This PR is included in version 1.3.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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[apancutt]

Shouldn't the return type be a Promise? i.e.

  declare function JsonSchemaToOpenapiSchema<T = Record<string | number, any>>(
    schema: Record<string | number, any>,
    options?: JsonSchemaToOpenapiSchema.Options
- ): T;
+ ): Promise<T>;