feat(BA-3170): Add ScalingGroup layer service logic, and implement pagination support

[jopemachine]

resolves #6977 (BA-3170)

Checklist: (if applicable)

• Mention to the original issue

[Copilot]

Pull request overview

This PR implements a new ScalingGroup service layer with repository pattern and pagination support, following the established architecture patterns in the codebase. The implementation adds search functionality for scaling groups with comprehensive test coverage at both the service and repository layers.

Key Changes

• Implements a three-layer architecture (service, repository, db_source) for scaling group operations
• Adds pagination support using the Querier infrastructure with OffsetPagination
• Integrates the new repository into the main Repositories class with proper resilience policies

Reviewed changes

Copilot reviewed 18 out of 21 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/ai/backend/manager/data/scaling_group/types.py	Adds ScalingGroupListResult type for paginated search results
src/ai/backend/manager/models/scaling_group.py	Adds to_dataclass() method to convert database rows to domain models
src/ai/backend/manager/repositories/scaling_group/db_source/db_source.py	Implements database operations for scaling group queries with pagination
src/ai/backend/manager/repositories/scaling_group/db_source/init.py	Exports ScalingGroupDBSource
src/ai/backend/manager/repositories/scaling_group/repository.py	Implements repository layer with resilience policies
src/ai/backend/manager/repositories/scaling_group/repositories.py	Factory class for creating scaling group repositories
src/ai/backend/manager/repositories/scaling_group/init.py	Exports ScalingGroupRepository
src/ai/backend/manager/repositories/repositories.py	Integrates scaling group repositories into main repository collection
src/ai/backend/manager/services/scaling_group/actions/base.py	Defines base action class for scaling group operations
src/ai/backend/manager/services/scaling_group/actions/list_scaling_groups.py	Implements search action and result types
src/ai/backend/manager/services/scaling_group/service.py	Implements service layer orchestrating repository operations
src/ai/backend/manager/services/scaling_group/processors.py	Implements action processors for scaling group operations
src/ai/backend/common/metrics/metric.py	Adds SCALING_GROUP_REPOSITORY layer type for metrics
tests/manager/repositories/scaling_group/test_scaling_group_repository.py	Comprehensive repository tests with various pagination scenarios
tests/manager/services/scaling_group/test_scaling_group_service.py	Service layer tests with mocked dependencies
tests/manager/repositories/scaling_group/BUILD	Build configuration for repository tests
tests/manager/services/scaling_group/BUILD	Build configuration for service tests
changes/6985.feature.md	Changelog entry describing the feature

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[Copilot]

Type mismatch: wsproxy_addr and wsproxy_api_token are nullable in the database model but ScalingGroupData expects non-nullable str types. This conversion will fail at runtime when these fields are None. Update ScalingGroupData to have Optional[str] for these fields or handle None values here.