fix: prevent inconsistent result error on update with ignore_all_server_changes

[maxtwardowski]

Summary

Update does not respect ignore_all_server_changes, causing "Provider produced inconsistent result after apply" when update_data changes a field that the server echoes back.

This is the same class of bug as #356 (which fixes ignore_server_additions), but for the ignore_all_server_changes code path.

Problem

ModifyPlan correctly preserves api_data and api_response from prior state when ignore_all_server_changes = true — telling Terraform these computed attributes won't change during apply.

However, Update unconditionally calls setResourceModelData, which overwrites api_data and api_response with values from the server response (either from the write response or the subsequent GET). When the update changes a field (e.g. name), the server returns the new value, creating a mismatch between what the plan promised and what the apply produced:

Error: Provider produced inconsistent result after apply

.api_data["name"]: was cty.StringVal("old"), but now cty.StringVal("new").

This makes ignore_all_server_changes incompatible with update_data for any field the server echoes back.

Reproduction

resource "restapi_object" "example" {
  path                      = "/api/resources"
  update_method             = "PATCH"
  ignore_all_server_changes = true

  data = jsonencode({
    name       = var.name
    secret_key = var.secret  # sensitive, only needed on creation
  })

  update_data = jsonencode({
    name = var.name
  })

  lifecycle {
    ignore_changes = [data]
  }
}

1. terraform apply — creates the resource successfully.
2. Change var.name and run terraform apply — plan correctly shows only update_data changing.
3. Apply fails with "Provider produced inconsistent result".

Fix

In Update, when ignore_all_server_changes is true, preserve api_data and api_response from prior state instead of overwriting them from the server response. This mirrors the existing pattern in ModifyPlan.

Test plan

• Added TestAccRestApiObject_IgnoreAllServerChanges_Update — creates a resource with ignore_all_server_changes = true and update_data, then changes update_data in a second step. Without the fix, step 2 fails with "Provider produced inconsistent result".
• Existing TestAccRestApiObject_IgnoreAllServerChanges still passes.
• Full test suite passes.