test: add high-priority tests for polling and certificate upload

- Add comprehensive tests for NfeClient.pollUntilComplete() (19 tests)
  * Test successful polling with multiple attempts
  * Test URL path extraction from full URLs and relative paths
  * Test timeout handling and error detection
  * Test recovery from temporary network errors
  * Test polling options validation

- Add createAndWait() tests to ServiceInvoicesResource (15 tests)
  * Test synchronous response (201) without polling
  * Test async response (202) with automatic polling
  * Test polling timeout and processing failures
  * Test custom polling options
  * Add getStatus() and createBatch() tests

- Add uploadCertificate() tests to CompaniesResource (15 tests)
  * Test certificate upload with Buffer and password
  * Test FormData creation and usage
  * Test custom filename handling
  * Test error propagation
  * Add getCertificateStatus(), findByTaxNumber(), and batch tests

- Add client-polling integration tests (12 tests)
  * Test end-to-end invoice creation workflow
  * Test progressive status changes
  * Test network error recovery during polling
  * Test concurrent invoice creation
  * Test real-world NFE.io scenarios

Coverage: ~50 new tests covering critical business logic
Status: 78 passing / 79 total (98.7%)
Impact: Eliminates critical gaps in polling and certificate upload

Author: andrekutianski