RVV updated for 128 and 256 bit platforms and fp16 intrinsics.

[adcastel]

This commit includes the extended rvv backend that I employed in the PDP and ISC workshop papers. It has been tested in 4 different RISC-V devices (Xuantie c906, c908, c910, and Banana PI F3)

[codecov]

Codecov Report

Attention: Patch coverage is 14.28571% with 6 lines in your changes missing coverage. Please review.

Project coverage is 88.34%. Comparing base (c2b48e4) to head (62e8960).

Files with missing lines	Patch %	Lines
src/exo/platforms/rvv.py	14.28%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #787      +/-   ##
==========================================
- Coverage   88.36%   88.34%   -0.03%     
==========================================
  Files          97       97              
  Lines       21809    21816       +7     
==========================================
+ Hits        19272    19273       +1     
- Misses       2537     2543       +6     

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