Logging a double-edge match at warning level (vs. info for a single edge)
makes it easy to spot an unexpected crop in the field, since two edges
matching at once is a much stronger signal of genuine baked-in padding than
one edge coinciding with real all-black content.
Also adds test/test_vegas_plugin_adapter.py covering _strip_scroll_padding's
branch logic: leading-only, trailing-only, both-edges, no-match, degenerate
all-black, missing/undersized display_width, and the info-vs-warning log level.