[oheliav]

Fixes #1251.

The go helpers in minView and maxView now return a StrictPair instead of a lazy tuple, so the rebuilt set is constructed right away instead of being left as a thunk. The signBranch case also forces the result of binCheckL/binCheckR before wrapping it in Just.

After the change, the Core for the go worker returns the rebuilt Bin/Tip/Nil directly in the unboxed tuple, with no lazy case left in the second component.

Benchmarks (intset-benchmarks, GHC 9.10.3, aarch64-osx):

benchmark	before	after	change
deleteMin	39.1 ns	19.5 ns	-50%
deleteMax	11.8 ns	6.84 ns	-41%
delete	42.5 μs	39.7 μs	same (doesn't use minView, for comparison)

intset-properties and intset-strictness-properties pass.

[treeowl]

How does this compare to IntMap? Do we want to produce the Just before descending the tree?