feat(task): implement GraphResolver with fan-in cycle pruning and migrate monorepo to Task System v3

[kyasbal]

Summary

This PR implements the new GraphResolver with priority-based fan-in cycle pruning and completes the monorepo migration to Task System v3 as part of epic/task-system-v3.

Key Changes

• 4-Phase GraphResolver (pkg/core/task):
  • Phase 1 (Mandatory Dependency Closure): BFS anchor discovery expanding required point-to-point and fan-in dependencies.
  • Phase 2 (Fan-In Candidate Binding): Binds candidate fan-in dependencies by tag and dependency scope with WithTagPriority support.
  • Phase 3 (Optional Binding & Mandatory 1:1 Edges): Evaluates optional point-to-point dependencies against the active graph and builds mandatory 1:1 edges.
  • Phase 3.5 (Fan-In Cycle Resolution, Pruning & Edge Deduplication): Detects circular fan-in dependencies, enforces AllowMultiStageExecution label requirements, checks for ambiguous priority ties, and deterministically prunes lower-priority cyclic fan-in edges when higher-priority bootstrap producers exist.
  • Phase 4 (Topological Sorting): Executes Kahn's algorithm over the resolved DAG to produce a deterministic execution order in TaskSet.
• Runner & Taskbase Modernization (pkg/core/inspection, pkg/core/task):
  • Updated LocalRunner to execute ResolveGraph, track concrete TaskEdge metadata, and manage memory lifecycle.
  • Modernized TaskBase, InventoryTask, and parser tasks to adopt the new Dependency model and edge attributes.
• Monorepo Inspection Task Migration (pkg/task/inspection):
  • Migrated all inspection tasks, parsers, and subgraphs across GCP, GKE, Composer, and OSS cluster packages to the v3 task interfaces and builder primitives.

Testing

• Exhaustive table-driven unit tests for GraphResolver and cycle resolution in graphresolver_test.go and graphresolver_cycle_test.go.
• Test cases covering priority-based pruning (1-hop, self-loop, and multi-hop transitive cycles), fail-fast error conditions (ambiguous priority ties, missing multi-stage label, lack of bootstrap producer), edge attribute deduplication/upgrades, and 100-iteration random shuffle invariance.
• All backend unit tests pass cleanly across the monorepo (make test-go).

[gemini-code-assist]

Code Review

This pull request refactors the task graph resolution mechanism by replacing the iterative GraphResolver with a deterministic 4.5-phase resolution algorithm (ResolveGraph). It introduces structured Dependency descriptors (such as point-to-point and fan-in tags with varying scopes) to replace taskid.UntypedTaskReference, adds robust cycle detection with priority-based pruning, and migrates the inventory system to a demand-driven tag-based approach. Additionally, the LocalRunner is optimized to clean up intermediate results before releasing waiter locks to prevent peak heap bloat. Feedback on the changes suggests standardizing on the coretask import alias instead of common_task in several form builder files to maintain code consistency.