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fix(math): make sinh overflow-threshold boundary inclusive

The sinh near-overflow branch used a strict `<` comparison against the
overflow threshold 0x408633ce8fb9f87d (|x| ~= 710.4758600739439). The
fdlibm `e_sinh.c` reference treats this boundary as inclusive: at exactly
the threshold value sinh is still finite (~1.7977e308, just below
DBL_MAX), so it must take the scaled-exp branch rather than fall through
to `x * shuge` and overflow.

Before this fix, sinh(710.4758600739439) returned +/-Infinity, while cosh
at the same point correctly returns a finite value.

Change `<` to `<=`, matching the reference and the analogous cosh branch,
and add a regression test that builds the exact threshold from a Double
hex-float literal (0x1.633ce8fb9f87dp9) so it cannot be weakened by
decimal rounding, covering both signs plus a larger value that must still
overflow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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