Improve support for CAdd

[NoureldinYosri]

This is a followup PR to #864 that

• adds a notebook for CAdd
• fixes classical action and adds classical action tests
• replaces the decomposition. The old decomposition is buggy and failed classical tests. Instead I use a simple decomposition that uses $n$ ancillas.
• adds tests for decomposition and symbolic costs

PS: we should probably replace this decomposition with the old one when we fix the bug in the old one.

[mpharrigan]

Let's track somewhere the task that Add().controlled() returns this bloq

[NoureldinYosri]

I created #1278 to track making Add.controlled() return CAdd