Fix project acceptance import state

[IlyaasK]

Summary

• Stop persisting command-import state over an already-managed project.
• Keep strict imported-state verification in an isolated Terraform state.
• Verify declarative import produces a no-op plan in a separate import-block
  step.

Why

The live project acceptance test failed before exercising provider import because
ImportStatePersist reused state that already contained kernel_project.test.
Terraform correctly rejected importing another object at the managed address.

The default command-import test uses isolated state and
ImportStateVerify compares the imported attributes with the prior resource
state. The import-block step independently removes the copied state entry and
requires the configured import plan to be a no-op.

Tests

• gofmt -l internal/resources/project
• go test -short -timeout=2m ./internal/resources/project
• go vet ./internal/resources/project
• git diff --check
• Acceptance workflow:
  • Project acceptance passed in 25 seconds.
  • Browser pool acceptance passed in 35 seconds with
    KERNEL_ALT_PROJECT_ID configured.

Scope

No provider behavior, schema, API calls, SDK usage, or production import logic
changes.