fix(linglong): stop migration clobbering refs and mis-ordering versions

[Metastarx]

Summary

The legacy ref migration in libs/linglong/src/linglong/repo/migrate.cpp could corrupt already-migrated refs. The dedup step appended each legacy ref onto one shared prefix string, and because std::string::append mutates its receiver, every lookup after the first used a key that could never exist; refs whose stable: counterpart was already present were migrated again and the existing commits (and their layer symlinks) were overwritten. The same file's version comparison was not lexicographic either, so 2.0.0 sorted below 1.7.0 and a repository newer than 1.7.0 could re-run the legacy migration. I rebuilt the lookup key from a fresh, const prefix on every iteration and replaced the comparison with a component-by-component lexicographic order, then added regression tests for an all-prefixed repository, a partial migration, and a 2.0.0 version file that must skip the migration.

Changes

libs/linglong/src/linglong/repo/migrate.cpp        |  33 +++-
 .../ll-tests/src/linglong/repo/migrate_test.cpp    | 210 +++++++++++++++++++++
 2 files changed, 240 insertions(+), 3 deletions(-)

Verification

ctest --test-dir build-release --output-on-failure - passed (100% tests passed, 0 tests failed out of 738)

Checklist

• I ran the verification described above
• The change is minimal and includes no unrelated files
• The repository contribution guidelines were followed

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[deepin-ci-robot]

Hi @Metastarx. Thanks for your PR.

I'm waiting for a OpenAtom-Linyaps member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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