Implement Clone for LazySegtree and discuss the Debug Implementation

[NotLeonian]

Implement the Clone trait for LazySegtree.
Since both MapMonoid::F and <F::M as Monoid>::S have the Clone constraint, it can be derived.

Additionally, LazySegtree already has a Debug implementation, but there is a comment saying // TODO is it useful? .
It may be necessary to discuss whether to implement Debug for FenwickTree and Segtree based on this implementation.

[NotLeonian]

The Debug trait implementation might be better if it follows the format discussed in FenwickTree #145 to keep things consistent.

Also, personally, I feel that it might be a bit confusing for users if the fmt function does not display the struct name.