fix: detect fixes in OSV Semver ranges (#1930)

* fix: detect fixes in OSV Semver ranges

OSV Scanner emits dependency fix intervals as SEMVER ranges. Accept those alongside ECOSYSTEM ranges while retaining the conservative single-interval requirement.

* fix: reject mixed OSV range types

Count every matching range before accepting a fixed version. Unsupported ranges mixed with Semver or Ecosystem data now retain the conservative mitigation decision.