fix: use subgraphOrNil across graph backends

[Kyle-Ye]

Expose the optional subgraph getter as subgraphOrNil across OpenAttributeGraph and its graph adapters. Remove the Compute shim that always returned nil so callers use Compute's existing getter.

Update the compatibility test call and the DPF CI fallback revision to include the matching Swift API rename. The C symbol remains unchanged.

Dependency

• DarwinPrivateFrameworks#73 (merged)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 31.83%. Comparing base (1d8e762) to head (5d1cfd6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #244   +/-   ##
=======================================
  Coverage   31.83%   31.83%           
=======================================
  Files          71       71           
  Lines        2629     2629           
=======================================
  Hits          837      837           
  Misses       1792     1792           

Flag	Coverage Δ
macos	10.15% <ø> (ø)
ubuntu	12.03% <ø> (ø)

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[tuist]

🛠️ Tuist Run Report 🛠️

Tests 🧪

Scheme	Status	Ran test modules	Commit
OpenAttributeGraph-Package	❌	4	144d67a91

Failed Tests ❌

• OpenAttributeGraph-Package: 1 failed test (View all)

• testMode3() · OpenAttributeGraphCompatibilityTests · DebugServerTests
  (host → "169.254.61.167").hasPrefix("192.168")

Builds 🔨

Scheme	Status	Duration	Commit
OpenAttributeGraph	✅	4.1s	144d67a91
OpenAttributeGraph-Package	✅	13.1s	144d67a91