detect: fix multi inspect buffer issue; clean up

detect: fix multi inspect buffer issue; clean up

Fix multi inspect buffer API causing cleanup logic in the single
inspect buffer paths. This could lead to a buffer overrun in the
"to clear" logic.

Multi buffers now use InspectionBufferSetupMulti instead of
InspectionBuffer. This is enforced by a check in debug validation.

Simplify the multi inspect buffer setup code and update the callers.