Fix RISC-V JIT stack store and cast check bugs

[am11]

Storing a contained constant to a stack local built it in the reserved
register, which the emitter reused to form large frame offsets, so the
stored value was clobbered. Small-int overflow checks on int sources
compared all 64 bits, although the upper half of an int register is
not guaranteed to be sign-extended. Complex Tan/Tanh tests now honor
the NaN payload policy for zero signs derived from NaN inputs.

Fixes #130562

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