feat: implement TypeFlavor and enhance inline assembly operand handling

[LunaStev]

This PR introduces a significant enhancement to Wave's type system and LLVM backend by implementing "Type Flavors." This architectural change allows the compiler to distinguish between high-level value representations and ABI-compliant types required for C FFI. Additionally, the inline assembly (asm) engine has been overhauled to handle register bit-width normalization and sign-aware operand promotion, making system-level programming more predictable and robust.

Key Changes

1. Type Flavoring & ABI Compatibility

• TypeFlavor Enum: Introduced TypeFlavor in types.rs with two variants: Value (internal representation) and AbiC (C ABI compliant).
• Context-Aware Mapping: Updated wave_type_to_llvm_type to adjust types based on the flavor. For example, when using AbiC, Booleans are now emitted as i8 rather than i1 to ensure correct parameter passing when calling external C functions.
• System-Wide Integration: Refactored all codegen entry points—including function signatures, struct definitions, and variable declarations—to utilize the appropriate flavor based on the context.

2. Robust Inline Assembly (asm) Improvements

• Sign-Aware Input Promotion: Implemented automatic integer promotion for assembly inputs. The compiler now uses the infer_signedness utility to decide between sign-extension (sext) and zero-extension (zext) when promoting values to match target register widths.
• Output Normalization: Added logic to handle bit-width mismatches for assembly outputs. If a target register (e.g., a 64-bit 'r' constraint) returns a value larger than the destination variable, the backend now correctly truncates or extends the result.
• Enhanced Coercion: Refactored coerce_basic_value_for_store to support a wider range of conversions for assembly results, including complex integer-to-pointer and float-to-int mappings.

3. LLVM Backend Utilities

• Recursive Literals: Added support for recursive literal generation when the expected target is an ArrayType. This allows complex nested initializers to be generated more reliably.
• Signedness Inference: Introduced the infer_signedness helper to assist the codegen engine in making mathematically correct decisions during type promotion and comparison.

4. Maintenance & Hygiene

• Cleaned up unused imports across the parser and codegen submodules.
• Improved internal documentation and error messages within the backend to assist with debugging complex IR generation scenarios.

Impact

Before: Passing a bool to a C function might result in i1 being passed, which some C ABIs handle inconsistently.
After: With TypeFlavor::AbiC, the bool is correctly passed as an i8 (0 or 1), matching standard C expectations.

Benefits

• FFI Reliability: Better compatibility with external C libraries by respecting standard ABI type widths.
• Low-Level Safety: Predictable register handling in asm blocks prevents subtle bugs related to sign-extension and bit-truncation.
• Code Quality: A more modular and context-aware type system simplifies future backend development.