`?:`-operator/`CondOp` with scalar condition calculates both then/else-expressions

The conditional operator `cond ? then-value : else-value` in DaphneDSL accepts scalars and matrices for the condition (see DaphneDSL language reference). In DaphneIR, this operator is represented by `daphne::CondOp`. If the condition is a matrix, `CondOp` is lowered to a kernel call. If the condition is a scalar, we don't need kernels, but rewrite the `daphne::CondOp` to a `scf::IfOp` in `CondOp::canonicalize()`.

Currently, in the rewritten IR, the then/else-expressions are evaluated before the `IfOp`, not inside it's branches. This could be good (e.g., if the then/else-values have common subexpressions with other code) or bad (e.g., if they are expensive to compute).

**It would be good to further investigate this, especially to avoid very expensive scenarios.**

Please search for #486 in the codebase.

Search the codebase for #486 and start with CondOp::canonicalize(), the DaphneDSL language reference, and the DaphneIR lowering to scf::IfOp. Trace when the scalar condition's then- and else-expressions are evaluated, then establish the expected evaluation behavior and how to avoid unnecessarily expensive computation.

Written by the indexing model from the issue text.