Add E2E integration tests

[albertodebortoli]

Pull Request Title

Add E2E integration tests

Description

• Adds end-to-end integration tests that exercise real state transitions across multiple components (Installer, Uninstaller, Unlinker, LinkedToolsLister) in full lifecycle scenarios.
• Unit tests cover 98.4% line coverage but no test composed multiple components together through a full install → unlink/uninstall → reinstall cycle. These E2E tests fill that gap.
• Uses LinkedToolsLister as the primary verification oracle, mirroring what luca linked reports to the user.
• Two new Lucafile fixtures with unique desiredBinaryName per tool (and bare URLs, no extension) ensure each tool produces a distinct symlink — avoiding the overwrite problem present in existing fixtures where all tools share the same binaryPath basename.

Type of Change

• Feature
• Bug fix
• Maintenance / Refactor
• Documentation
• CI / Tooling
• Other (specify)

How Has This Been Tested?

All 6 new E2E tests pass, and the full suite (160 tests) passes with no regressions.

swift test --filter E2ETests
swift test

• Added / updated unit tests
• Tested on macOS (arch: arm64)

Screenshots / Demo (if applicable)

Suite E2ETests passed after 0.043 seconds.
Test run with 160 tests in 26 suites passed after 0.139 seconds.

Checklist

• Swift code builds locally (swift build)
• Tests pass locally (swift test)
• Code style / formatting respected
• Documentation updated (README / comments)
• Version / tag alignment considered (if release related)
• PR title follows conventional style (optional)

CI Considerations

• Affects build time notably
• Requires new secrets / env vars
• Alters release process

Breaking Changes?

• No

Additional Notes

New files:

• Tests/Fixtures/Lucafiles/Lucafile_e2e_full.yml — 3 tools (MockToolA 1.0.0, MockToolB 2.0.0, MockToolC 3.0.0) each with a unique desiredBinaryName
• Tests/Fixtures/Lucafiles/Lucafile_e2e_subset.yml — MockToolB + MockToolC only, used to trigger orphan detection against MockToolA
• Tests/E2E/E2ETests.swift — 6 tests covering: uninstall leaves broken symlink, unlink preserves cache, unlink then reinstall restores link, subset spec orphans tool, unlink one leaves others intact, uninstall then reinstall re-downloads