feat(phase-9.75g-0): Implement BID-FFI Day 3 - Box type integration

- Implement BID Box Bridge interface for Nyash Box <-> BID Handle conversion
- Add StringBox BID bridge implementation with handle/TLV support
- Add IntegerBox BID bridge implementation with handle/TLV support
- Implement BoxRegistry for managing Box instances and handles
- Add comprehensive tests for StringBox/IntegerBox BID round-trip
- Extract helper functions for string/integer value extraction

Everything is Box philosophy shines through unified BID integration! 🎉

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/bid/mod.rs

@@ -6,12 +6,14 @@ pub mod tlv;
 pub mod error;
 pub mod metadata;
 pub mod plugin_api;
+pub mod bridge;
 
 pub use types::*;
 pub use tlv::*;
 pub use error::*;
 pub use metadata::*;
 pub use plugin_api::*;
+pub use bridge::*;
 
 /// BID-1 version constant
 pub const BID_VERSION: u16 = 1;