perf: Add AppendProtocols for a an allocation free to get the protocols

While looking at Kubo benchmarks, if you are using connection filters you allocate ~200MiB/s in the Protocols code path.

This new method allows to give some preallocated memory in a slice, and it will be reused instead of allocating more.

```
goos: linux
goarch: amd64
pkg: github.com/multiformats/go-multiaddr
cpu: AMD Ryzen 5 3600 6-Core Processor
BenchmarkProtocols-12          	 3779694	       312.0 ns/op	     640 B/op	       1 allocs/op
BenchmarkAppendProtocols-12    	26105854	        43.13 ns/op	       0 B/op	       0 allocs/op
```

component.go

@@ -77,6 +77,10 @@ func (c *Component) Protocols() []Protocol {
 	return []Protocol{c.protocol}
 }
 
+func (c *Component) AppendProtocols(ps []Protocol) []Protocol {
+	return append(ps, c.protocol)
+}
+
 func (c *Component) Decapsulate(o Multiaddr) Multiaddr {
 	if c.Equal(o) {
 		return nil

interface.go

@@ -41,6 +41,10 @@ type Multiaddr interface {
 	// will panic if protocol code incorrect (and bytes accessed incorrectly)
 	Protocols() []Protocol
 
+	// AppendProtocols is similar to Protocols but it will reuse the extra
+	// capacity in the slice first, this allows to prevent allocations.
+	AppendProtocols([]Protocol) []Protocol
+
 	// Encapsulate wraps this Multiaddr around another. For example:
 	//
 	//      /ip4/1.2.3.4 encapsulate /tcp/80 = /ip4/1.2.3.4/tcp/80

makeslice.go

@@ -0,0 +1,9 @@
+package multiaddr
+
+// makeSlice is like make([]T, len) but it perform a class size capacity
+// extension. In other words, if the allocation gets rounded to a bigger
+// allocation class, instead of wasting the unused space it is gonna return it
+// as extra capacity.
+func makeSlice[T any](len int) []T {
+	return append([]T(nil), make([]T, len)...)
+}

multiaddr.go

@@ -106,10 +106,13 @@ func (m *multiaddr) UnmarshalJSON(data []byte) error {
 	return err
 }
 
-// Protocols returns the list of protocols this Multiaddr has.
-// will panic in case we access bytes incorrectly.
 func (m *multiaddr) Protocols() []Protocol {
-	ps := make([]Protocol, 0, 8)
+	return m.AppendProtocols(makeSlice[Protocol](8)[:0])
+}
+
+// AppendProtocols returns the list of protocols this Multiaddr has.
+// will panic in case we access bytes incorrectly.
+func (m *multiaddr) AppendProtocols(ps []Protocol) []Protocol {
 	b := m.bytes
 	for len(b) > 0 {
 		code, n, err := ReadVarintCode(b)

multiaddr_test.go

@@ -347,7 +347,7 @@ func TestBytesSplitAndJoin(t *testing.T) {
 func TestProtocols(t *testing.T) {
 	m, err := NewMultiaddr("/ip4/127.0.0.1/udp/1234")
 	if err != nil {
-		t.Error("failed to construct", "/ip4/127.0.0.1/udp/1234")
+		t.Fatal("failed to construct", "/ip4/127.0.0.1/udp/1234")
 	}
 
 	ps := m.Protocols()
@@ -361,6 +361,48 @@ func TestProtocols(t *testing.T) {
 		t.Error("failed to get udp protocol")
 	}
 
+	ps = m.AppendProtocols(ps)
+	if ps[2].Code != ProtocolWithName("ip4").Code {
+		t.Error(ps[2], ProtocolWithName("ip4"))
+		t.Error("failed to get ip4 protocol")
+	}
+
+	if ps[3].Code != ProtocolWithName("udp").Code {
+		t.Error(ps[3], ProtocolWithName("udp"))
+		t.Error("failed to get udp protocol")
+	}
+}
+
+var ProtocolSink []Protocol
+
+func BenchmarkProtocols(b *testing.B) {
+	m, err := NewMultiaddr("/ip4/127.0.0.1/udp/1234")
+	if err != nil {
+		b.Fatal("failed to construct", "/ip4/127.0.0.1/udp/1234")
+	}
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	var ps []Protocol
+	for i := b.N; i != 0; i-- {
+		ps = m.Protocols()
+	}
+	ProtocolSink = ps
+}
+
+func BenchmarkAppendProtocols(b *testing.B) {
+	m, err := NewMultiaddr("/ip4/127.0.0.1/udp/1234")
+	if err != nil {
+		b.Fatal("failed to construct", "/ip4/127.0.0.1/udp/1234")
+	}
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	var ps []Protocol
+	for i := b.N; i != 0; i-- {
+		ps = m.AppendProtocols(ps[:0])
+	}
+	ProtocolSink = ps
 }
 
 func TestProtocolsWithString(t *testing.T) {