feat: make policy length limits configurable per engine (#624)

- Add PolicyLengthConfig struct with max_col, max_file_bytes, and
  max_lines fields, replacing hardcoded constants in the lexer.
- Add Engine::set_policy_length_config and clear_policy_length_config
  to allow callers to override the default limits.
- Add Source::from_contents_with_limits and from_file_with_limits for
  direct Source construction with custom limits; existing from_contents
  and from_file signatures are preserved using defaults.
- Add tests for default rejection, custom limits, and engine plumbing.
- Add bindings for C, C++, Python, WASM/JS, Java, Ruby, C#, Go

src/lib.rs

@@ -167,6 +167,7 @@ pub use engine::Engine;
 pub use lexer::Source;
 pub use policy_info::PolicyInfo;
 pub use utils::limits::LimitError;
+pub use utils::limits::PolicyLengthConfig;
 #[cfg(all(feature = "allocator-memory-limits", not(miri)))]
 pub use utils::limits::{
     check_global_memory_limit, enforce_memory_limit, flush_thread_memory_counters,