Added ast tree to simplify expression lifetime management

[lamarrr]

Description

This merge request follows up on #10744.
It attempts to simplify managing expressions by adding a class called an ast tree. The ast tree manages and holds related expressions together. When the tree is destroyed, all the expressions are also destroyed. Ideally we would use a bump allocator for allocating the expressions instead of std::vector<std::unique_ptr<expression>>.

We'd also ideally use a cuda::std::inplace_vector for storing the operands of the operation class, but that's in a newer version of CCCL.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[wence-]

Trivial comment suggestions (my approval has no power here)