Refactor: Consolidate tests by pattern (post-#12)

Prerequisites

• #12 must be completed first
• All existing tests must pass after #12

Scope

Consolidate test files by pattern, eliminating duplication across checkers.

Current State

testdata/
├── metatest/tests/      # 70+ JSON files
└── src/
    ├── goroutine/       # duplicated patterns
    ├── errgroup/        # duplicated patterns
    ├── waitgroup/       # duplicated patterns
    ├── conc/            # duplicated patterns
    └── gotask/

Target State

testdata/src/
├── patterns/
│   ├── closure_captures/
│   │   ├── literal.go
│   │   ├── variable.go
│   │   ├── higher_order.go
│   │   └── ssa_tracking.go
│   ├── callback_receives/
│   │   └── ...
│   └── deriver/
│       └── ...
└── gostmt/
    └── special_cases.go

Tasks

• Remove JSON metadata files
• Consolidate duplicate test cases by pattern
• Keep pattern-specific edge cases
• Update test runner configuration
• Remove See also comment requirements

Dependency

Blocked by #12 - implementation refactoring must complete first to ensure test stability during migration.

Related

• #12 SSA-based pattern registry architecture
• #9 Add support for sourcegraph/conc
• #10 Add support for panjf2000/ants

First complete #12 and confirm all existing tests pass. Review the testdata/metatest/tests JSON files and duplicated cases under testdata/src/{goroutine,errgroup,waitgroup,conc,gotask}; use the target patterns layout as the migration guide. Done means JSON metadata and See also requirements are removed, duplicate cases are consolidated while edge cases remain, and the test runner configuration passes.