[mlir][scf] Fix trip count signedness and overflow in SCF Utils (#178782)

Change `getConstLoopTripCounts` to return `SmallVector<llvm::APInt>`
instead
of `SmallVector<int64_t>` to properly handle signedness and prevent
potential
overflow issues. Update all call sites to use APInt methods and uint64_t
for
intermediate calculations.
- Use APInt::isOne() instead of direct comparison with 1
- Store trip counts in uint64_t to avoid overflow in modulo operations
- Remove TODOs about signedness and overflow issues that are now fixed
Fixes #178506

GitOrigin-RevId: 02358c0fcf3c0849813b6502fb539847c4ad8f2b