Rust Code generation

[loic-fejoz]

Summary

This PR introduces a Rust Code Generation feature to fsdr-cli, enabling any DSP flowgraph (from csdr commands or .grc files) to be exported as a standalone, Rust source file.

The implementation follows the Futamura projection concept: the flowgraph is partially evaluated, complex parameters (like FIR taps) are pre-computed, and the resulting physical data is baked directly into the generated code as literals. This eliminates runtime overhead for graph construction and parameter resolution.

Key Changes

• Abstract Backend: Introduced the FsdrBackend trait to decouple semantic flowgraph resolution from physical instantiation.
• Dual-Backend System:
  • RuntimeBackend: Builds a live FutureSDR flowgraph for immediate CLI execution.
  • CodegenBackend: Emits optimized Rust source code using quote!.
• fsdr-cli-macros Crate: A new proc-macro sub-crate providing the #[fsdr_instantiate] attribute. This ensures a "One Source of Truth" by automatically
  generating both runtime and codegen versions of a block's constructor.
• Global Refactor: Migrated all ~40 block converters in src/grc/converter/ to the new generic backend architecture.
• CLI Integration: Added the --generate flag to both csdr and grc commands.
• Optimized Baking: Implemented wrappers like CodegenTaps and CodegenPattern to bake complex types into generated source code as standard Rust vectors.

Usage Example

Export an optimized standalone Rust program from a complex pipeline

fsdr-cli csdr --generate src/my_dsp_app.rs convert_u8_f ! shift_addition_cc 0.01 ! fmdemod_quadri_cf ! dump_f

Verification

• Added integration tests in tests/codegen.rs covering basic and complex flowgraph chains.
• Verified that generated code for complex FM demodulation pipelines passes cargo check and correctly resolves all internal dependencies.
• Updated AGENTS.md and agent_docs/ with the new architectural standards.