gds: register stream to warm compat init

[nclack]

Fixes #118.

Approach

In compat mode, libcufile lazily allocates per-stream state on the first cuFileReadAsync, and that lazy init races against itself. The passing test in the same file happens to enqueue a cuLaunchHostFunc barrier before the first read, which serializes the stream enough to mask the race. The failing test goes straight into cuFileReadAsync on an empty stream and SEGVs ~4% of the time deep inside libcufile.

cuFile already exposes the hook for this: cuFileStreamRegister "allocates resources needed to support cuFile operations asynchronously for the cuda stream" — i.e. exactly the lazy state that was racing. Calling it eagerly when damacy adopts a stream removes the race window. The matching cuFileStreamDeregister is required before cuStreamDestroy per the cuFile contract.

Change

In src/store/store_fs_gds.c:

• dlsym-bind cuFileStreamRegister / cuFileStreamDeregister as optional symbols (graceful no-op on older libcufile that doesn't ship them).
• store_fs_gds_set_stream: deregister any previously-set stream, then register the new one. First cuFileReadAsync now finds per-stream state already allocated.
• gds_destroy: deregister after the existing cuStreamSynchronize, before the caller's cuStreamDestroy.

Verification

• cmake --build build clean.
• 100× loop of CUFILE_FORCE_COMPAT_MODE=true ./build/tests/test_store_fs_gds: 0 failures (was ~4/100).
• Full ctest: 26/26 pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.71%. Comparing base (5f9226d) to head (27a726c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #119      +/-   ##
==========================================
+ Coverage   55.64%   55.71%   +0.07%     
==========================================
  Files          49       49              
  Lines        6903     6903              
  Branches     1233     1233              
==========================================
+ Hits         3841     3846       +5     
+ Misses       2585     2582       -3     
+ Partials      477      475       -2     

Flag	Coverage Δ
unittests	55.71% <ø> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.
see 7 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.