realm: add cuda-gather-dma refactoring

[apryakhin]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 22.22222% with 91 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.23%. Comparing base (b9df3d6) to head (b06e9f3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/realm/transfer/transfer.cc	15.95%	78 Missing and 1 partial ⚠️
src/realm/transfer/channel.cc	42.85%	6 Missing and 2 partials ⚠️
src/realm/transfer/channel.h	0.00%	2 Missing ⚠️
src/realm/transfer/transfer.h	0.00%	1 Missing ⚠️
tests/unit_tests/lowlevel_dma_test.cc	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #326      +/-   ##
==========================================
+ Coverage   27.15%   27.23%   +0.07%     
==========================================
  Files         190      190              
  Lines       39174    39125      -49     
  Branches    14166    14348     +182     
==========================================
+ Hits        10638    10654      +16     
- Misses      27240    28076     +836     
+ Partials     1296      395     -901     

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