feat(fuzz): add cargo-fuzz targets and fix 3 parser bugs

Add 5 fuzz targets for stackforge-core parsers:
- packet_parse: full Packet::parse() entry point
- dns_layer: DNS name decompression, question/RR parsing
- tls_layer: TLS record, handshake, SSLv2 parsing
- http_layers: HTTP/1.x, HTTP/2 frames, HPACK decoding
- field_access: direct field accessors across protocol layers

Bugs found and fixed by fuzzing:
- HPACK integer decode: arithmetic overflow in varint continuation
- MQTT variable-length integer: multiply overflow before bounds check
- ARP parser: off-by-one in length guard (offset+5 vs offset+6)

Author: AKOrojo

Cargo.lock

@@ -905,6 +905,10 @@ impl Layer for ArpLayer {
     fn extract_padding<'a>(&self, buf: &'a [u8]) -> (&'a [u8], &'a [u8]) {
         self.extract_padding(buf)
     }
+
+    fn field_names(&self) -> &'static [&'static str] {
+        ArpLayer::field_names()
+    }
 }
 
 // ============================================================================

crates/stackforge-core/src/layer/arp.rs

@@ -385,6 +385,10 @@ impl Layer for DhcpLayer {
         let d = self.data(buf);
         d.len()
     }
+
+    fn field_names(&self) -> &'static [&'static str] {
+        DHCP_FIELD_NAMES
+    }
 }
 
 /// Check if a UDP payload looks like a DHCP packet.

crates/stackforge-core/src/layer/dhcp/mod.rs

@@ -863,6 +863,10 @@ impl Layer for Ipv4Layer {
     fn extract_padding<'a>(&self, buf: &'a [u8]) -> (&'a [u8], &'a [u8]) {
         self.extract_padding(buf)
     }
+
+    fn field_names(&self) -> &'static [&'static str] {
+        Ipv4Layer::field_names()
+    }
 }
 
 #[cfg(test)]