These assertions can only trigger because of bugs in the bindings
implementation or in the C code and not because of bugs in calling code,
so using debug assertions is perfectly fine for them and reduces the
number of assertions inlined everywhere in release builds.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/1188>
This should be analogous to C struct initalizers where all unspecified
fields are initialized to zero. Without mut this reads a bit nicer as
well.
Note that two out of three structs have all members specified, hence
need no zero-initialization of the remainder at all.
They can actually be shared with multiple threads at the same time
safely as all functions requiring an immutable reference are
thread-safe.
OTOH TypeFind can't be shared safely between different threads as not
all implementations of the TypeFind struct are thread-safe.
