Reduce heap allocations (#42)

* pcap: reuse Frame memory

* slog: reduce heap allocations of addresses; also prevent heap alloc of dhcp options in pcap

* dns: heapless improvement; add StackAsync buffer for more heapless operation; start thinking of errors

* reuse function for reclaiming frames among all protocols for lower memory usage

* remove extraneous code

internal/slogattr.go

@@ -0,0 +1,22 @@
+package internal
+
+import (
+	"encoding/binary"
+	"log/slog"
+)
+
+// SlogAddr4 returns a slog.Attr for a 4-byte IPv4 address
+// packed into a uint64 without allocating a string.
+func SlogAddr4(key string, addr *[4]byte) slog.Attr {
+	u64Addr := uint64(binary.BigEndian.Uint32(addr[:]))
+	return slog.Uint64(key, u64Addr)
+}
+
+// SlogAddr6 returns a slog.Attr for a 6-byte hardware (MAC) address
+// packed into a uint64 without allocating a string.
+func SlogAddr6(key string, addr *[6]byte) slog.Attr {
+	var buf [8]byte
+	copy(buf[2:], addr[:])
+	u64Addr := binary.BigEndian.Uint64(buf[:])
+	return slog.Uint64(key, u64Addr)
+}