fix(sdk): update dependency dart to v3.9.4

[renovate]

This PR contains the following updates:

Package	Update	Change
dart (source)	patch	>=3.9.2 <4.0.0 → 3.9.4

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Release Notes

dart-lang/sdk (dart)

v3.9.4

Compare Source

Released on: 2025-09-30

Pub

• dart pub get --example will now resolve example/ folders in the
  entire workspace, not only in the root package.
  This fixes dart-lang/pub#4674 that made flutter pub get
  crash if the examples had not been resolved before resolving the workspace.

v3.9.3

Compare Source

Released on: 2025-09-09

Tools

Development JavaScript compiler (DDC)

• Fixes a pattern that could lead to exponentially slow compile times when
  static calls are deeply nested within a closure.
  When present this led to builds timing out or
  taking several minutes rather than several seconds.

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