Enhance executor interfaces

[chhwang]

• Support to explicitly set executor's stream
• Support data copy between ARK tensors and external CUDA arrays
• Support non-loop execution mode
• Minor fixes & interface updates

[codecov]

Codecov Report

Attention: Patch coverage is 91.39785% with 16 lines in your changes missing coverage. Please review.

Project coverage is 86.90%. Comparing base (1dd3c62) to head (d0b0432).
Report is 1 commits behind head on main.

Files	Patch %	Lines
ark/api/executor.cpp	91.41%	14 Missing ⚠️
python/ark/tensor.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #222      +/-   ##
==========================================
+ Coverage   86.61%   86.90%   +0.28%     
==========================================
  Files         117      117              
  Lines        5118     5177      +59     
==========================================
+ Hits         4433     4499      +66     
+ Misses        685      678       -7     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.