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/url.dict

@@ -0,0 +1,84 @@
+# AFL++ dictionary for URL fuzzing
+# This helps AFL++ generate more interesting mutations
+
+# URL schemes
+"http://"
+"https://"
+"ftp://"
+"file://"
+"mailto:"
+"data:"
+"ws://"
+"wss://"
+
+# Special characters
+":"
+"/"
+"?"
+"#"
+"@"
+"."
+"%"
+"["
+"]"
+
+# Authority separators
+"//"
+"@"
+
+# Port separators
+":80"
+":443"
+":8080"
+":3000"
+
+# Percent encoding
+"%20"
+"%2F"
+"%3A"
+"%00"
+"%FF"
+
+# IPv4 patterns
+"127.0.0.1"
+"192.168.1.1"
+"0.0.0.0"
+"255.255.255.255"
+
+# IPv6 patterns
+"::1"
+"::"
+"2001:db8::1"
+"::ffff:192.0.2.1"
+
+# Common paths
+"/index.html"
+"/api/v1"
+"/../"
+"/.."
+"/."
+
+# Common query strings
+"?query=value"
+"&"
+"="
+
+# Common fragments
+"#fragment"
+"#top"
+
+# Userinfo
+"user:password@"
+"user@"
+":password@"
+
+# Special values
+"localhost"
+"example.com"
+"example.org"
+
+# Whitespace
+"\t"
+"\n"
+"\r"
+" "