rkyv: Panic safety bugs in `InlineVec::clear` and `SerVec::clear` enable arbitrary code execution

InlineVec::clear and SerVec::clear in rkyv were not panic-safe. Both functions iterate over their elements and call dropinplace on each, updating self.len only after the loop. If an element's Drop implementation panics during the loop, self.len is left at its original value. A subsequent invocati...