feat(engine): Support barebones Mode for Engine

[rajeshgangireddy]

📝 Description

Implements #3095
Information about barebones is in the issue.

✨ Changes

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• 🚀 New feature (non-breaking change which adds functionality)
• 🐞 Bug fix (non-breaking change which fixes an issue)
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• 🧪 Tests (adding/modifying tests)
• 📚 Documentation update
• 📦 Build system changes
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• 🔒 Security update
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)

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[Copilot]

Pull request overview

This PR implements barebones mode support for the Engine, which allows running training/testing with minimal overhead by disabling checkpointing and logging while still preserving metric collection.

Key changes:

• Barebones mode disables automatic checkpoint creation during training
• Manual metric population ensures metrics are available in barebones mode despite disabled logging
• Test coverage added to verify metric consistency and checkpoint behavior between normal and barebones modes

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/anomalib/engine/engine.py	Disables checkpoint callback creation when barebones mode is enabled and injects logged metrics into test results
src/anomalib/metrics/evaluator.py	Manually updates trainer metrics in barebones mode to ensure availability in return values
tests/unit/engine/test_engine.py	Adds comprehensive test verifying metric consistency and checkpoint behavior in barebones mode

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Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

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