feat: Registry v2 artifact searcher

[BackendBits]

• feat: Add RegDef V2 validation with version detection

Detect version field in RegDef files and validate against V2 schema when version is 2.0. Use logger for validation messages and move schema paths to constants.

• feat: Add V2 cloud registry support for artifact searcher

• Add AuthConfig model for V2 authentication configuration
• Add version and auth_config fields to Registry model
• Add V2 routing in check_artifact_async with fallback to V1
• Add CloudAuthHelper for AWS/GCP cloud registry authentication
• Add environment credential loading for V2 cloud registries
• Add V2 cloud registry dependencies (boto3, google-auth)
• Add comprehensive tests for V2 models and routing

Preserves all V1 functionality including:

• Nexus detection and URL conversion
• Snapshot version resolution
• URL-based artifact search

• fix: V2 artifact searcher cleanup and improvements

• Simplified retry logic (2 retries, 5s fixed delay)

• Reduced timeouts to reasonable values (60s search, 120s download)

• Removed debug/diagnostic code

• Removed unnecessary test files

• Clean up code style

• fix: minor issues on v2

• fix: changes for v2 working with Auth_config as null or empty for Artifacotry/nexus

Pull Request

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