Add comprehensive fuzzing infrastructure for URL parser

This commit adds AFL++ (American Fuzzy Lop) fuzzing support to help find bugs,
crashes, and security vulnerabilities in the URL parser.

Changes:
- Add fuzz_afl.c: AFL++ fuzz target that tests all parser functions
  - url_parse() with different flag combinations
  - url_parse_ipv4() and url_parse_ipv6()
  - url_serialize(), url_percent_decode(), url_remove_white_space()

- Add build_afl.sh: Build script with AFL++ compiler detection
- Add run_afl.sh: Automated fuzzing script with result reporting
- Add url.dict: Dictionary file to guide AFL++ mutations

- Add corpus/: Seed inputs covering various URL patterns
  - Basic URLs, IPv4/IPv6, percent-encoding, relative paths
  - Edge cases and special schemes (file://, mailto:, etc.)

- Add FUZZING.md: Comprehensive documentation
  - Installation instructions
  - Quick start guide
  - Advanced usage (parallel fuzzing, sanitizers)
  - Troubleshooting tips

- Add fuzz.c: Standalone mutation-based fuzzer (no AFL++ required)
  - Useful for quick testing without installing AFL++
  - Implements various mutation strategies

tests/run_afl.sh

@@ -0,0 +1,86 @@
+#!/bin/bash
+# Run AFL++ fuzzing
+#
+# Usage:
+#   ./run_afl.sh [duration_in_minutes]
+#
+# Examples:
+#   ./run_afl.sh        # Run indefinitely (press Ctrl+C to stop)
+#   ./run_afl.sh 60     # Run for 60 minutes
+
+set -e
+
+# Check if fuzz target exists
+if [ ! -f "fuzz_afl" ]; then
+    echo "Error: fuzz_afl binary not found!"
+    echo "Please run ./build_afl.sh first"
+    exit 1
+fi
+
+# Check if AFL++ is installed
+if ! command -v afl-fuzz &> /dev/null; then
+    echo "Error: afl-fuzz not found!"
+    echo "Please install AFL++:"
+    echo "  sudo apt-get install afl++"
+    exit 1
+fi
+
+# Create output directory if it doesn't exist
+mkdir -p findings
+
+# Set AFL++ options for better performance
+export AFL_SKIP_CPUFREQ=1
+export AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES=1
+
+echo "Starting AFL++ fuzzing..."
+echo "Corpus directory: corpus/"
+echo "Output directory: findings/"
+echo ""
+echo "Press Ctrl+C to stop fuzzing"
+echo ""
+
+# Run AFL++ with optional timeout and dictionary
+DICT_ARG=""
+if [ -f "url.dict" ]; then
+    DICT_ARG="-x url.dict"
+    echo "Using dictionary: url.dict"
+fi
+
+if [ -n "$1" ]; then
+    timeout_sec=$((60 * $1))
+    echo "Running for $1 minutes ($timeout_sec seconds)"
+    timeout $timeout_sec afl-fuzz -i corpus/ -o findings/ $DICT_ARG -- ./fuzz_afl || true
+else
+    afl-fuzz -i corpus/ -o findings/ $DICT_ARG -- ./fuzz_afl
+fi
+
+echo ""
+echo "Fuzzing completed!"
+echo ""
+echo "Results:"
+echo "  Crashes: findings/default/crashes/"
+echo "  Hangs:   findings/default/hangs/"
+echo "  Queue:   findings/default/queue/"
+echo ""
+
+# Check for crashes
+if [ -d "findings/default/crashes" ]; then
+    num_crashes=$(find findings/default/crashes -type f ! -name 'README.txt' | wc -l)
+    if [ $num_crashes -gt 0 ]; then
+        echo "⚠️  Found $num_crashes crash(es)!"
+        echo "To reproduce a crash:"
+        echo "  ./fuzz_afl < findings/default/crashes/id:000000,*"
+    else
+        echo "✓ No crashes found"
+    fi
+fi
+
+# Check for hangs
+if [ -d "findings/default/hangs" ]; then
+    num_hangs=$(find findings/default/hangs -type f ! -name 'README.txt' | wc -l)
+    if [ $num_hangs -gt 0 ]; then
+        echo "⚠️  Found $num_hangs hang(s)!"
+    else
+        echo "✓ No hangs found"
+    fi
+fi