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/build_afl.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+# Build script for AFL++ fuzzing
+#
+# Prerequisites:
+#   - AFL++ installed (https://github.com/AFLplusplus/AFLplusplus)
+#
+# Install AFL++ on Ubuntu/Debian:
+#   sudo apt-get install afl++
+#
+# Or build from source:
+#   git clone https://github.com/AFLplusplus/AFLplusplus
+#   cd AFLplusplus
+#   make
+#   sudo make install
+
+set -e
+
+echo "Building fuzz target with AFL++..."
+
+# Try different AFL++ compilers in order of preference
+if command -v afl-clang-fast &> /dev/null; then
+    echo "Using afl-clang-fast (recommended)"
+    AFL_CC=afl-clang-fast
+elif command -v afl-gcc &> /dev/null; then
+    echo "Using afl-gcc"
+    AFL_CC=afl-gcc
+elif command -v afl-clang &> /dev/null; then
+    echo "Using afl-clang"
+    AFL_CC=afl-clang
+else
+    echo "Error: No AFL++ compiler found!"
+    echo "Please install AFL++ first:"
+    echo "  sudo apt-get install afl++"
+    echo "Or see: https://github.com/AFLplusplus/AFLplusplus"
+    exit 1
+fi
+
+# Build the fuzz target
+$AFL_CC -o fuzz_afl fuzz_afl.c ../url.c -Wall -Wextra -ggdb
+
+echo "Build successful! Binary: fuzz_afl"
+echo ""
+echo "To run fuzzing:"
+echo "  ./run_afl.sh"