Add C Language Plugin Support

[topheman]

This PR introduces support for WebAssembly Component Model plugins written in C, expanding the plugin ecosystem beyond Rust implementations.

You will be able to run this kind of command in the REPL: echoc foo which will act like the echo plugin (made in rust).

✨ Key Features

• C Plugin Infrastructure: Added complete toolchain and build system for C-based plugins
• Echo Plugin Implementation: Created a C version of the echo plugin (c_modules/plugin-echo/component.c) as a reference implementation
• WASI SDK Integration: Integrated wasi-sdk for compiling C code to WebAssembly components
• CI/CD Updates: Added wasi-sdk download step to CI workflows for both Rust host and web host
• Web Host Support: Added jco transpile integration to run C plugins in the browser

🔧 Technical Implementation

• Memory Management: Proper C string handling with null-termination and memory allocation
• WIT Bindgen Integration: Generated C bindings from WIT interface definitions
• Build System: Added just tasks for C plugin development (just dl-wasi-sdk, just c-wit-bindgen-plugins)
• Testing: Added end-to-end tests for C plugins with full CI integration
• Web Transpilation: C plugins are compiled to WASM and jco transpile provides JavaScript bindings for browser execution

📚 Documentation

• Comprehensive C plugin development guide in c_modules/README.md
• Updated main README with C plugin information
• Added development workflow documentation

🧪 Testing

• Added e2e tests for C echo plugin functionality
• Split test infrastructure for better organization
• CI integration for C plugin builds

📦 Resources

C Tooling

• From the WebAssembly Component Model section for C tooling
• WASI SDK
• WIT Bindgen

This feature enables developers to write plugins in C, providing more language options for the WebAssembly Component Model REPL ecosystem while maintaining the same plugin interface and functionality as Rust implementations. C plugins now work seamlessly across both CLI and web hosts.