Make stable bloom filter threadsafe

antireplay/stable_bloom_filter.go

 package antireplay
 
 import (
+	"sync"
+
 	"github.com/9seconds/mtg/v2/mtglib"
 	"github.com/OneOfOne/xxhash"
 	boom "github.com/tylertreat/BoomFilters"
 
 type stableBloomFilter struct {
 	filter boom.StableBloomFilter
+	mutex  sync.Mutex
 }
 
 func (s *stableBloomFilter) SeenBefore(digest []byte) bool {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
 	return s.filter.TestAndAdd(digest)
 }