Add nvbench-based benchmarks for the fltflt data types (#1124)

* Add nvbench-based benchmarks for the fltflt data types

Add several benchmarks that are built via -DMATX_BUILD_BENCHMARKS=ON.
Also add bench/scripts/run_fltflt_benchmarks.py, which runs the fltflt
benchmarks and summarizes the results. Example results when running
on RTX PRO 6000 Blackwell Server Edition are as follows:

Performance relative to single-precision (float = 1.0x baseline)
Higher values indicate slower performance

Benchmark       float        double       fltflt       fltflt vs dbl
------------------------------------------------------------------
add             1.00x        71.10x       28.84x       2.47x
sub             1.00x        71.11x       28.85x       2.46x
mul             1.00x        71.17x       10.15x       7.01x
div             1.00x        52.63x       5.85x        8.99x
sqrt            1.00x        52.40x       3.89x        13.48x
abs             1.00x        2.17x        2.15x        1.01x
fma             1.00x        71.13x       25.36x       2.81x
madd            1.00x        71.14x       38.78x       1.83x

-------------------------------------------------------------------

Note that addition and subtration and only ~2.5x faster using fltflt than
fp64. Multiplication, division, and square root are significantly faster.
Future updates may improve addition performance, but potentially at an
accuracy cost, so the changes will likely be opt-in.

Signed-off-by: Thomas Benson <tbenson@nvidia.com>

* Add adding guards in run_fltflt_benchmarks.py parsing

Signed-off-by: Thomas Benson <tbenson@nvidia.com>

---------

Signed-off-by: Thomas Benson <tbenson@nvidia.com>

Author: tbensonatl