Improve fuzzing coverage of yajl-ruby

[jsnv-dev]

This pull request adds new fuzzers to improve the fuzzing coverage of yajl-ruby, focusing on JSON processing and buffer manipulation functions:

• string_encode_fuzzer: Tests string encoding functionality with different HTML safety modes and buffer operations including truncation
• parse_complete_fuzzer: Tests JSON parsing completion handling with various input states and error conditions
• lex_peek_fuzzer: Tests lexer peeking functionality with different token types and positions
• error_string_fuzzer: Tests error message generation and handling across different error types and verbosity levels

[github-actions]

jsnv-dev is a new contributor to projects/yajl-ruby. The PR must be approved by known contributors before it can be merged. The past contributors are: inferno-chromium, devtty1er, Dor1s, titanous (unverified)

[jsnv-dev]

Hi @inferno-chromium, @devtty1er, @Dor1s, @titanous. Can you help in reviewing this PR when you have spare time? Thank you!

[titanous]

@jsnv-dev Have you checked if yajl-ruby would be willing to carry these fuzz targets upstream?

[jsnv-dev]

@jsnv-dev Have you checked if yajl-ruby would be willing to carry these fuzz targets upstream?

I haven't checked with them. I can check with them, but should I also move the existing fuzzer in the oss-fuzz project folder?

[titanous]

Yeah if they are up for it, it’s ideal if fuzz targets are maintained upstream.