Some unit tests depends on external services

[tdruez]

Tests such as:
tests/test_fetch.py::test_resolve_purl_using_purl2url
tests/test_package.py::test_cocoapods_packages

needs an internet connection to fetch data on external services.
Instead, the test should all pass even when isolated from internet. Use mock instead.

Also, a default timeout should be enforced on all requests calls.