Tuple types that goes across the hardware restriction

[eopXD]

This issue is a placeholder to help us keep track of the idea and revisit after v1.0.

Currently we have tuple types that matches conforms to the hardware restriction (that is, NFIELD * LMUL <= 8). Complex math functions may have the need to return two LMUL=8 values. We should be able to achieve this in a software point of view.

[kito-cheng]

Two use case in my mind:

• Complex math functions: https://en.cppreference.com/w/c/numeric/complex
• sincos: https://man7.org/linux/man-pages/man3/sincos.3.html