deallocate

        fn deallocate(self: *Self, allocator: Allocator) void {
            if (self.metadata == null) return;

            const header_align = @alignOf(Header);
            const key_align = if (@sizeOf(K) == 0) 1 else @alignOf(K);
            const val_align = if (@sizeOf(V) == 0) 1 else @alignOf(V);
            const max_align = comptime @max(header_align, key_align, val_align);

            const cap: usize = self.capacity();
            const meta_size = @sizeOf(Header) + cap * @sizeOf(Metadata);
            comptime assert(@alignOf(Metadata) == 1);

            const keys_start = std.mem.alignForward(usize, meta_size, key_align);
            const keys_end = keys_start + cap * @sizeOf(K);

            const vals_start = std.mem.alignForward(usize, keys_end, val_align);
            const vals_end = vals_start + cap * @sizeOf(V);

            const total_size = std.mem.alignForward(usize, vals_end, max_align);

            const slice = @as([*]align(max_align) u8, @ptrCast(@alignCast(self.header())))[0..total_size];
            allocator.free(slice);

            self.metadata = null;
            self.available = 0;
        }