Add ctrl system for LinearCombination

[anurudhp]

Fixes the nightly test fail (qualtran/bloqs/block_encoding/chebyshev_polynomial_test.py::test_scaled_chebyshev_even_tensors)

Added two cost tests to ensure that no C[And] etc are in the call graph.

[mpharrigan]

Thanks for doing this. When I investigated, I traced the ultimate problem to trying to do Controlled(LessThanEqual) as the proximate operation that tries to do C[And]. Would implementing LessThanEqual.controlled() fix the bug or is there something else wrong that requires the fix to be at the level of LinearCombination ?

(note that we do have CLinearDepthGreaterThan)

[anurudhp]

I think so, but LinearCombination uses StatePreparationAliasSampling (which uses LessThanEqual) in a compute-uncompute pair, so this override (i.e. only control the select) results in a lower cost.

[mpharrigan]

Very well, thank you!