1.4.1 — Fix loadModel(downloadIfNeeded: false) not compiling in Release

Fixed

• loadModel(downloadIfNeeded: false) failed to compile in a Release build. The isResident check it depends
  on (added in 1.4.0) was accidentally scoped inside an #if DEBUG block meant only for test seams. Any consumer
  archiving a Release build while using this method — new in 1.4.0 — hit "value of type 'MLXModelRuntime' has no
  member 'isResident'". swift test/xcodebuild test always run Debug, so this was invisible until an actual
  Release archive. isResident now compiles in both configurations; the remaining test-seam accessors stay
  #if DEBUG-only.

Upgrading from 1.4.0

• Required if you call loadModel(downloadIfNeeded: false) (AICompleteChat's AppEnvironment, and anything
  following the "Adopt MLXModelManager for downloads" guidance in the 1.4.0 notes) and ship a Release/Archive
  build. No code changes.