[ty] Go back to reduced BDDs for constraint sets (#26142)
I've been wanting to do this for awhile!
Several months ago, https://github.com/astral-sh/ruff/pull/21744 updated
our BDDs to be "quasi-reduced", as a way to eliminate some
nondeterminism in our diagnostic output, but at the cost of creating
larger BDDs.
We now have enough other protections in place to eliminate the
nondeterminism in other ways (in particular, the `source_order`s that we
store in our BDD nodes, and the fact that we assign constraint IDs
locally in each `ConstraintSetBuilder` in a way that depends only on
source order).
So this PR reverts back to the more standard reduction semantics. This
is complicated by the fact that we migrated to _ternary_ decision
diagrams (TDD) in https://github.com/astral-sh/ruff/pull/23881, which
means the standard BDD reduction rule (`if_true == if_false → return
if_true`) isn't valid. But there are some other locally checkable
reduction rules that we can still implement.
