fix: stop versioned go imports colliding on version segment

[ivov]

Go packages whose import path ends in a version suffix (/v2, /v3, ...) now resolve to their real package name instead of the version segment. Previously, importing two such packages reported an Import conflict.

import "go:github.com/pion/sdp/v3"
import "go:github.com/pion/dtls/v3"

fn main() {
  let _ = sdp.SessionDescription {}
  let _ = dtls.Config {}
}

Paths that are actyally named v1/v2 (e.g. k8s.io/api/core/v1) keep working, and a project's own modules are unaffected.

Fix #803