[IMP] account_ebics - Add unit tests

Add 97 tests:

- account_ebics: order numbers, camt and CFONB split per account,
  journal lookup, duplicate statements, download and upload wizards,
  key initialisation (INI/HIA/HPB), passphrase change, admin orders.
- account_ebics_batch: scheduled import, import log, reprocess.
- account_ebics_payment_order / account_ebics_batch_payment: upload of
  the payment file and link to the payment document.
- account_ebics_statement_import_test (new, test-only, not to install
  in production): installs the OCA camt and CFONB parsers in CI and
  runs the end-to-end statement import.

The bank is simulated by patching ebics.xfer._setup_client, or the
fintech client classes for the key initialisation; keys, certificates
and the INI letter are real, created in a temporary directory.

account_ebics/tests/samples/invalid.xml

@@ -0,0 +1 @@
+this is not an xml document