resources deleted out-of-bounds are not recreated

[ermul]

Steps to Reproduce

I'm using rootly_form_field here, but I expect it could be reproduced with any resource.
versions:
terraform: 1.9.8
terraform-provider-rootly: 2.19.1

1. Create a new form_field resource (Copied from examples/resources/rootly_form_field/resource.tf and added an output for the ID)

resource "rootly_form_field" "regions_affected" {
  name       = "Regions affected"
  kind       = "custom"
  input_kind = "multi_select"
  shown      = ["web_new_incident_form", "web_update_incident_form"]
  required   = ["web_new_incident_form", "web_update_incident_form"]
}

resource "rootly_form_field_option" "asia" {
  form_field_id = rootly_form_field.regions_affected.id
  value         = "Asia"
}

resource "rootly_form_field_option" "europe" {
  form_field_id = rootly_form_field.regions_affected.id
  value         = "Europe"
}

resource "rootly_form_field_option" "north_america" {
  form_field_id = rootly_form_field.regions_affected.id
  value         = "North America"
}

output form_field_id {
  value = rootly_form_field.regions_affected.id
}

3. Delete the form_field via API

curl --request DELETE \
  --url 'https://api.rootly.com/v1/form_fields/<form-field-id>' \
  --header "Authorization: Bearer $ROOTLY_TOKEN"

4. Run terraform apply -refresh-only -auto-approve -input=false -lock=false -json

Current Behavior

Fails with Error reading form_field: <form-field-id>

Expected Behavior

Refresh removes the form_field that was deleted so that it will be recreated.

Cause

I believe I've identified a problem with error handling that's causing this issue.

• The generated client code is catching RequestErrors returned by the API, and returning a new error. i.e. currently:

  if err != nil {
    return nil, errors.Errorf("Error building request: %s", err.Error())
  }

• In the generated resources e.g. provider/resource_form_field.go

  	item, err := c.GetFormField(d.Id())
    if err != nil {
    	// In the case of a NotFoundError, it means the resource may have been removed upstream
    	// We just remove it from the state.
    	if _, ok := err.(client.NotFoundError); ok && !d.IsNewResource() {
    		tflog.Warn(ctx, fmt.Sprintf("FormField (%s) not found, removing from state", d.Id()))
    		d.SetId("")
    		return nil
    	}
  
    	return diag.Errorf("Error reading form_field: %s", d.Id())
    }

Since a new error is being returned in the client code, this type assertion will always fail: err.(client.NotFoundError)