Code cleanup & bug fixes

[chhwang]

• Clean up some unused code
• Remove ark_utils.h
• Add host-only data types ark::half_t and ark::bfloat16_t
• Better detect index overflows from kernel code
• Fix barriers for 2-warp ops
• Fix wrong ldims after reshape
• Detect invalid paddings during scheduling
• Other minor updates

[codecov]

Codecov Report

Merging #158 (be4a42d) into main (da5aeb4) will decrease coverage by 1.09%.
Report is 1 commits behind head on main.
The diff coverage is 62.31%.

❗ Current head be4a42d differs from pull request most recent head 6d7a365. Consider uploading reports for the commit 6d7a365 to get more accurate results

@@            Coverage Diff             @@
##             main     #158      +/-   ##
==========================================
- Coverage   71.69%   70.60%   -1.09%     
==========================================
  Files          89       91       +2     
  Lines        6634     6851     +217     
==========================================
+ Hits         4756     4837      +81     
- Misses       1878     2014     +136     

Files	Coverage Δ
ark/executor.cc	95.12% <ø> (ø)
ark/gpu/gpu_comm_sw.cc	72.22% <ø> (ø)
ark/gpu/gpu_mgr.cc	78.19% <100.00%> (ø)
ark/include/ark.h	100.00% <ø> (ø)
ark/ops/ops_matmul.cc	90.72% <100.00%> (+0.18%)	⬆️
ark/ops/ops_scale.cc	92.85% <100.00%> (ø)
ark/ops/ops_sharding.cc	92.59% <100.00%> (+0.28%)	⬆️
ark/random.h	100.00% <100.00%> (ø)
ark/sched/sched_op.cc	60.60% <ø> (-15.11%)	⬇️
ark/file_io.cc	86.17% <66.66%> (ø)
... and 13 more

... and 6 files with indirect coverage changes