Add test coverage for duplicate license file prevention

[Copilot]

Addresses review feedback requesting tests for the break statement added in a0ea75c that prevents duplicate acknowledgements when packages contain multiple license files (LICENSE, LICENSE.txt, LICENSE.md).

Changes

• DuplicateLicenseFileTests.swift: Three test cases validating the fix:

  • Single package with multiple license files → one acknowledgement using first match (LICENSE)
  • Multiple packages with varying license files → one acknowledgement per package, correct priority
  • Explicit test demonstrating bug without break → duplicate entries created

• scanForLicenses(shouldBreak:): Helper method simulating CLI scanning logic using temporary SPM checkout directories, tests both correct and buggy behavior paths

Test Approach

// Given: Package with LICENSE, LICENSE.txt, LICENSE.md
let packageDir = packageCachePath.appendingPathComponent("TestPackage")
try createLicenseFiles(in: packageDir)

// When: Scanning with break (correct behavior)
let acknowledgements = try scanForLicenses(shouldBreak: true)

// Then: Only one entry, uses first match
XCTAssertEqual(acknowledgements.count, 1)
XCTAssertEqual(acknowledgements[0].license, licenseFromLICENSE)

Tests compile on Linux but require macOS to run (SwiftUI dependency in package).

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[MartinP7r]

Closing in favor of #42 which applies these tests rebased onto current main. Cleaned up slightly (removed redundant comments, simplified helper). All tests pass.