Extend overloads for arithmetic operators of ExprPtr

[Krzmbrzl]

Note: I didn't add overloads for +=, -= and friends for now. They could be added once we have a need for them…

/CC @ajay-mk: these should allow you to shorten your expressions in the manuscript

[ajay-mk]

Thanks @Krzmbrzl.

Just one question: why change from std::constructible_from to std::is_constructible_v?

PS: I did not mean to request changes, mouse slip :(

[Krzmbrzl]

Just one question: why change from std::constructible_from to std::is_constructible_v?

That wasn't intentional. Looking at the docs, these should be functionally equivalent though 👀

[ajay-mk]

That wasn't intentional. Looking at the docs, these should be functionally equivalent though 👀

That's what I thought. I was just wondering if there’s any difference.