[Rust] Release 0.18.0

Added

• Custom keywords support. #379
• Expose JsonPointerNode that can be converted into JSONPointer.
  This is needed for the upcoming custom keyword support.

Changed

• Bump base64 to 0.22.
• Bump clap to 4.5.
• Bump fancy-regex to 0.13.
• Bump fraction to 0.15.
• Bump memchr to 2.7.
• Bump once_cell to 1.19.
• Bump percent-encoding to 2.3.
• Bump regex to 1.10.
• Bump url to 2.5.
• Build CLI only if the cli feature is enabled.
• BREAKING: Extend CompilationOptions to support more ways to define custom format checkers (for example in Python bindings).
  In turn, it changes ValidationErrorKind::Format to contain a String instead of a &'static str.

Fixed

• Incorrect schema_path when multiple errors coming from the $ref keyword #426

Performance

• Optimize building JSONPointer for validation errors by allocating the exact amount of memory needed.
• Avoid cloning path segments during validation.