[ty] normalize typevar bounds/constraints in cycles (#21800)
Fixes https://github.com/astral-sh/ty/issues/1587
## Summary
Perform cycle normalization on typevar bounds and constraints (similar
to how it was already done for typevar defaults) in order to ensure
convergence in cyclic cases.
There might be another fix here that could avoid the cycle in many more
cases, where we don't eagerly evaluate typevar bounds/constraints on
explicit specialization, but just accept the given specialization and
later evaluate to see whether we need to emit a diagnostic on it. But
the current fix here is sufficient to solve the problem and matches the
patterns we use to ensure cycle convergence elsewhere, so it seems good
for now; left a TODO for the other idea.
This fix is sufficient to make us not panic, but not sufficient to get
the semantics fully correct; see the TODOs in the tests. I have ideas
for fixing that as well, but it seems worth at least getting this in to
fix the panic.
## Test Plan
Test that previously panicked now does not.
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Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
