fix(memory): restore RegisteredMemoryContext::device, broken on main

[justinchuby]

main does not compile in the CUDA lane, and my own #1725 is what broke it. Flagging that first because it gates every PR currently open.

error[E0599]: no method named `device` found for struct `RegisteredMemoryContext`
  --> crates/onnx-runtime-ep-cuda/src/provider.rs:1163:30
error: could not compile `onnx-runtime-ep-cuda` (lib)
exit=101

First red at a2cd1e7bf; a2a61656f immediately before it is green. git show ab0880b69 (#1725) contains the removal.

What happened

#1725 rewrote the use list in manager.rs to pull in the pin-source types, and pub fn device was deleted along with it. Nothing in that PR required its removal — the underlying RegisteredProviderContext::device is untouched — so this restores the forwarder verbatim.

Why nothing caught it, which is the part worth keeping

Three independent things had to line up, and each is individually reasonable:

1. onnx-runtime-ep-cuda has exactly one caller of this method, and it compiles in exactly one job. Every lane that ran on feat(memory): pin the provider/context across a plugin's deferred release #1725 was blind to it by construction.
2. I verified feat(memory): pin the provider/context across a plugin's deferred release #1725 with cargo clippy --all-targets -- -D warnings on the three crates I had edited. That is a real check, and it is exactly the crate set that cannot observe this break. Editing crate A and verifying crate A is the natural thing to do and it is not sufficient when A is a library.
3. A pub method with no in-crate caller draws no dead_code warning. So deleting it was silent going out, and the breakage was silent coming back — until a job that most PRs never reach.

This is the same shape as the kv_commits_on_demand finding in #1631/#1632: several individually-sound reasons not to look, converging. I had that lesson in hand and still shipped this, so the lesson evidently was not "run clippy" — it was verify the reverse dependencies of a library change, not the library.

Verification — the lane's own command, not a proxy

cargo check -p onnx-runtime-ep-cuda -p onnx-runtime-python --features onnx-runtime-python/cuda

main  -> exit 101 (the E0599 above)
fixed -> exit 0

Negative control taken deliberately: I stashed the fix and re-ran on clean main to confirm the error returns, so this is demonstrably the cause rather than a change that merely happens to compile.

Both results reproduced locally on macOS aarch64 with no CUDA toolkit and no GPU. That matters — this was catchable on any developer machine, which means it was not a CUDA-hardware coverage gap.

Also clean: cargo fmt --all -- --check; clippy -D warnings on the governor; 67 + 34 + 5 governor tests; and the native-CUDA clippy lane from #1632.

Not fixed here

Mobius metadata packages is also red, with The process '/usr/bin/git' failed with exit code 1 and no compile error. Different failure, unrelated to this change, and I have not diagnosed it.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.11%. Comparing base (6fdc04d) to head (a65fc5d).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/onnx-runtime-memory-governor/src/manager.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1762      +/-   ##
==========================================
- Coverage   80.11%   80.11%   -0.01%     
==========================================
  Files         411      411              
  Lines      198646   198649       +3     
  Branches   198646   198649       +3     
==========================================
- Hits       159151   159146       -5     
- Misses      34094    34101       +7     
- Partials     5401     5402       +1     

Flag	Coverage Δ
cli-ort-linux	72.47% <ø> (ø)
cli-ort-windows	71.97% <ø> (ø)
mlas	85.10% <ø> (-0.10%)	⬇️
offline	80.24% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
crates/onnx-runtime-memory-governor/src/manager.rs	75.68% <0.00%> (-0.10%)	⬇️

... and 3 files with indirect coverage changes

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