Improve ssa shuffler fix args region

[clonker]

• introduces argsRange on target helper, inspired from SSA: Fix cycle in stack shuffler #16595 (comment)
• reachability-gated pushes/dups in fixArgsSlot:
  • previously, we'd sometimes push/dup slots that then immediately had to be popped again
  • add
    • canReachSomeUnfilledTarget(arg) checking if there is a swap-reachable slot wanting arg, and
    • prefixReachable checking that, after growing the stack, every misaligned prefix offset is still reachable
  • with these two utils, skip pushes/dups that would leave something stranded
• guarded fast path in fixArgsSlot:
  • guard the fast path (place the arg the target wants at the new top directly) but only under a stricter pushKeepsDeepPrefixReachable gate: every misaligned prefix offset must survive the grow plus one more op. this accounts for committing the slot to its final position right away, which means that fixing a deeper slot requires duping/pushing something else first if that slot is in its final position

[clonker]

here the guards are a bit strict perhaps. i managed to get rid of the regression in this particular case but that lead to overall worse results in the external contracts. ugh :)

[blishko]

It definitely shows potential, but let's see if we can minimize the regressions.

[blishko]

Why is this not true anymore?

[clonker]

previously, the fixArgsSlot couldn't refuse to grow and would, worst case, push junk. now it can refuse and ultimately yield NoAction in which case the invariant would be violated.

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