fix: fallback mode per file

[noomorph]

Fixes an edge case spotted on CI.

To reproduce on affected versions:

• Run test project with multiple workers
• Some test files should initialize properly, some others must fail while initializing the test environment
• Spectate weird errors like Metadata (undefined) is not an instance of TestFileMetadata from this place:

if (!(metadata instanceof Klass)) {
  throw new TypeError(`Metadata (${metadata?.id}) is not an instance of ${klassName}`);
}

[github-actions]

🎉 This PR is included in version 1.5.4 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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