pub fn push_back(&mut self, value: T) {
        if self.is_full() {
            self.grow();
        }

        let head = self.head;
        self.head = self.wrap_add(self.head, 1);
        unsafe { self.buffer_write(head, value) }
    }
Inserts an element at `index` within the `VecDeque`, shifting all elements with indices
greater than or equal to `index` towards the back.

Element at index 0 is the front of the queue.

# Panics

Pani
benchmarks/haystacks/code/rust-library.rs