FTP bugs have been the #1 recurring issue across releases (0.1.8+).
This adds a real implicit FTPS mock server and 67 test cases covering
every known failure mode — connection, upload, download, delete, storage
info, model-specific SSL behavior, async wrappers, and failure injection.
New files:
- mock_ftp_server.py: implicit FTPS server on pyftpdlib with failure injection
- conftest.py: FTP test fixtures (certs, server, client factory)
- test_bambu_ftp.py: 67 tests across 10 test classes
Also adds pyOpenSSL to requirements-dev.txt (needed by pyftpdlib
TLS_FTPHandler in the Docker test image).
