chore: improve svu maintenance path

[otjdiepluong]

Summary:

• Add a small table-driven edge-case unit test in internal/svu/svu_test.go for FindNext / version-bump behavior on inputs that already contain a pre-release or build-metadata suffix (e.g. v1.2.3-rc1, v1.2.3+meta) combined with a forced --minor/--patch bump, asserting the suffix is stripped and the bump is applied exactly once. Pure additive test, no behavior change.
• Keep the change narrow so it is straightforward to review.

Notes:

• I kept this scoped to the relevant implementation and tests.