Improve YUM test coverage for ListInstalled, Clean, and GetPackageInfo methods

Start with manager/yum and the fixture-based patterns in behavior_test.go, then review MockCommandRunner and the authentic outputs under testing/fixtures/yum/. Run go test ./manager/yum -cover first. Done means comprehensive behavior tests cover ListInstalled, Clean, and GetPackageInfo, pass in CI/CD, and maintain or improve overall YUM coverage.

Problem Statement

YUM package manager has 0% test coverage for three critical methods:

• ListInstalled() - Currently 0% coverage
• Clean() - Currently 0% coverage
• GetPackageInfo() - Currently 0% coverage

Current Test Coverage Status

From recent go test ./manager/yum -cover results:

• Overall YUM coverage: 69.4%
• Good coverage: enhancePackagesWithStatus (89.5%), Find (76.9%)
• Missing coverage: ListInstalled, Clean, GetPackageInfo (0% each)

Acceptance Criteria

• Add comprehensive tests for ListInstalled() method
• Add comprehensive tests for Clean() method
• Add comprehensive tests for GetPackageInfo() method
• Use existing fixture-based testing patterns
• Follow testing philosophy: focus on behavior and contracts
• Maintain or improve overall YUM test coverage percentage
• All new tests pass in CI/CD pipeline

Implementation Approach

1. Use existing patterns: Follow established fixture-based testing in behavior_test.go
2. Leverage CommandRunner mocking: Use MockCommandRunner for unit tests
3. Real fixture data: Use authentic YUM command outputs from testing/fixtures/yum/
4. Cross-platform testing: Ensure tests work in Docker environments

Test Strategy

• ListInstalled: Test parsing of yum list installed output with various package states
• Clean: Test cache cleanup operations and output parsing
• GetPackageInfo: Test detailed package information retrieval and parsing

Priority

High Priority - These are core YUM operations that need test coverage for reliability and maintainability.

Related Issues

• Part of overall test coverage improvement initiative
• Follows CommandRunner architecture established in Issue #20
• Uses patterns proven successful in APT package manager testing