ensureTotalCapacityPrecise

pub fn ensureTotalCapacityPrecise(self: *Self, new_capacity: usize) !void {
    if (self.capacity() >= new_capacity) return;

    const old_memory = self.allocatedSlice();
    const new_memory = try self.allocator.realloc(old_memory, new_capacity);
    self.items.ptr = new_memory.ptr;
    self.cap = new_memory.len;
}