Package-level declarations

What an application may tune about the libass module. Nothing here is needed for it to work: adding the dependency installs the typesetter, and the engine routes every ASS and SSA track through it. These knobs exist for the platforms whose libass cannot find fonts by itself.

Whole-document rendering, one call per picture, for tools and tests.

libass as the engine's SubtitleTypesetter: a container header or a whole script goes in, one event per packet follows, and every render answers positioned premultiplied RGBA images in the output surface's own pixels.

The discovery entry. Public with a no-argument constructor because ServiceLoader needs both.