feat: add typeKey option to preserve resource type in deserialized objects

[SBoudrias]

Summary

This PR adds a typeKey option that allows preserving the JSON:API resource type in deserialized objects. This is useful when you need to know the original type of a resource after deserialization, especially when dealing with polymorphic relationships.

Deserialization

When typeKey is specified, the resource type is included in the output using the specified key name:

import { deserialize } from 'jsonapi-fractal'

const response = {
  data: {
    type: 'users',
    id: '1',
    attributes: { firstName: 'Joe' }
  }
}

deserialize(response, { typeKey: 'type' })
// Returns: { type: 'users', id: '1', firstName: 'Joe' }

This works for:

• Main resources
• Array of resources
• Included relationships
• Relationships not in the included array (returns { id, [typeKey]: type })

Serialization

When serializing with typeKey:

• The typeKey attribute is automatically removed from the output (so it doesn't appear in attributes)
• Validates that idKey and typeKey are different
• Validates that the typeKey value matches the specified type (if present in entity)

import { serialize } from 'jsonapi-fractal'

const entity = { id: '1', type: 'users', firstName: 'Joe' }

serialize(entity, 'users', { typeKey: 'type' })
// Returns: { data: { type: 'users', id: '1', attributes: { firstName: 'Joe' } } }
// Note: 'type' is stripped from attributes

Test plan

• Added tests for deserialization with typeKey
• Added tests for serialization with typeKey
• Added tests for error cases (idKey === typeKey, mismatched type values)
• All existing tests pass
• Lint passes
• Build passes

[github-actions]

This PR is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 15 days.

[SBoudrias]

I can't remove the label myself. Would really like to see this get in. Let me know if you want me to change anything.

That being said, I understand it's not been modified in 6 months. Hoping the project isn't dead.

[github-actions]

This PR is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 15 days.

[SBoudrias]

Still would like to get this in 🥹