implement a memory-optimized time.Time replacement (#5334)

* implement a memory-optimized time.Time replacement

* monotime: properly handle systems with bad timer resolution (Windows)

* monotime: simplify Since

path_manager.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/quic-go/quic-go/internal/ackhandler"
+	"github.com/quic-go/quic-go/internal/monotime"
 	"github.com/quic-go/quic-go/internal/protocol"
 	"github.com/quic-go/quic-go/internal/utils"
 	"github.com/quic-go/quic-go/internal/wire"
@@ -30,7 +31,7 @@ const pathTimeout = 5 * time.Second
 type path struct {
 	id             pathID
 	addr           net.Addr
-	lastPacketTime time.Time
+	lastPacketTime monotime.Time
 	pathChallenge  [8]byte
 	validated      bool
 	rcvdNonProbing bool
@@ -64,7 +65,7 @@ func newPathManager(
 // May return nil.
 func (pm *pathManager) HandlePacket(
 	remoteAddr net.Addr,
-	t time.Time,
+	t monotime.Time,
 	pathChallenge *wire.PathChallengeFrame, // may be nil if the packet didn't contain a PATH_CHALLENGE
 	isNonProbing bool,
 ) (_ protocol.ConnectionID, _ []ackhandler.Frame, shouldSwitch bool) {