OK, so here's what I can see from the repo:
Current state: The repo is on v2 (the README says "This is version 2 of Quamina"), the latest release on GitHub is v2.0.0 (Jan 21, 2026), and all the source files are in the root directory — no /v2 subdirectory. The package quamina declarations across the .go files all use package quamina with no /v2 in the imports.
The problem is exactly what Marius described. The go.mod almost certainly still says:
module quamina.net/go/quamina