Use the session's verify when it is not passed explicitly

[allburov]

Fixes #500.

Passing a session with TLS verification disabled had no effect:

session = requests.Session()
session.verify = False
path = ArtifactoryPath("https://artifactory.local/artifactory/repo", session=session)
# requests were still made with verify=True

ArtifactoryPath defaulted verify to True and passed it to every request explicitly. Requests gives a request-level argument precedence over the session's own setting, so session.verify was always discarded.

Now verify falls back to the session when it is not given, in both constructors. The precedence becomes: explicit verify= → config file entry → session.verify → True. Callers who pass no session are unaffected, and a session that never set verify still yields True, since that is the default in requests.

[beliaev-maksim]

thanks!
lgtm