Add cpp-libp2p fuzzing project

[vah13]

Summary

• Added fuzzing infrastructure for cpp-libp2p library
• Includes 6 fuzzers targeting different components: multiaddress parsing, multibase decoding, multihash parsing, multiselect parser, and message read/write operations
• Configured build scripts and Dockerfile for OSS-Fuzz integration

Fuzzers included

• multiaddress_parse_fuzzer.cc - Tests multiaddress parsing functionality
• multibase_decode_fuzzer.cc - Tests multibase decoding
• multihash_parse_fuzzer.cc - Tests multihash parsing
• multiselect_parser_fuzzer.cc - Tests multiselect protocol parser
• message_read_writer_bigendian_read_len_fuzzer.cc - Tests message reader with bigendian length
• message_read_writer_bigendian_write_uaf_fuzzer.cc - Tests message writer for UAF bugs

[github-actions]

vah13 is integrating a new project:
- Main repo: https://github.com/libp2p/cpp-libp2p
- Criticality score: 0.35879