feat(api): add NumPackages to mirrors/repos/snapshots list responses

add API response wrappers with NumPackages derived from RefList length; keep show endpoint payloads unchanged for backward compatibility; add API tests for list endpoint NumPackages; update swagger response schemas for list endpoints

api/package_count_response.go

@@ -0,0 +1,30 @@
+package api
+
+import "github.com/aptly-dev/aptly/deb"
+
+type remoteRepoResponse struct {
+	*deb.RemoteRepo
+	NumPackages int `json:"NumPackages"`
+}
+
+type localRepoResponse struct {
+	*deb.LocalRepo
+	NumPackages int `json:"NumPackages"`
+}
+
+type snapshotResponse struct {
+	*deb.Snapshot
+	NumPackages int `json:"NumPackages"`
+}
+
+func newRemoteRepoResponse(repo *deb.RemoteRepo) remoteRepoResponse {
+	return remoteRepoResponse{RemoteRepo: repo, NumPackages: repo.NumPackages()}
+}
+
+func newLocalRepoResponse(repo *deb.LocalRepo) localRepoResponse {
+	return localRepoResponse{LocalRepo: repo, NumPackages: repo.NumPackages()}
+}
+
+func newSnapshotResponse(snapshot *deb.Snapshot) snapshotResponse {
+	return snapshotResponse{Snapshot: snapshot, NumPackages: snapshot.NumPackages()}
+}