unistore: move continue to the resource package (#101206)

* minor improvements to tests

* move continue token

* update sql backend

pkg/storage/unified/sql/continue.go

@@ -1,32 +0,0 @@
-package sql
-
-import (
-	"encoding/base64"
-	"encoding/json"
-	"fmt"
-)
-
-type ContinueToken struct {
-	StartOffset     int64 `json:"o"`
-	ResourceVersion int64 `json:"v"`
-}
-
-func (c ContinueToken) String() string {
-	b, _ := json.Marshal(c)
-	return base64.StdEncoding.EncodeToString(b)
-}
-
-func GetContinueToken(token string) (*ContinueToken, error) {
-	continueVal, err := base64.StdEncoding.DecodeString(token)
-	if err != nil {
-		return nil, fmt.Errorf("error decoding continue token")
-	}
-
-	t := &ContinueToken{}
-	err = json.Unmarshal(continueVal, t)
-	if err != nil {
-		return nil, err
-	}
-
-	return t, nil
-}