feat: implement input() statement and L-value generation

[LunaStev]

This PR introduces the input() statement to support interactive console applications and performs a significant refactor of the expression code generation logic. By separating L-value (address) generation from R-value (value) generation, the compiler now supports more complex assignment targets and memory-modifying operations.

Key Changes

1. Interactive input() Statement

• AST/Parser: Added StatementNode::Input and implemented parse_input to support input("format", targets...) syntax.
• Format Validation: The parser now ensures the number of placeholders in the format string matches the number of provided arguments.
• LLVM Implementation:
  • Added wave_format_to_scanf to bridge Wave format strings with C-style scanf.
  • Generated IR to call scanf, passing the memory addresses of target variables.
  • Error Handling: Added runtime checks to ensure scanf successfully reads the expected number of arguments; otherwise, the program exits with code 1.

2. L-Value Generation & Codegen Refactor

• Architectural Reorganization: Split the monolithic expression.rs into a module containing mod.rs, rvalue.rs, and lvalue.rs.
• L-Value System (generate_lvalue_ir): Implemented dedicated logic to retrieve the memory address of an expression. This supports:
  • Variables and pointer dereferences.
  • Nested Accessors: Complex paths like arr[i], obj.field, and even combined forms like (deref p).field[idx].
  • Ensures type correctness when navigating through pointers and struct offsets.

3. Interactive Runtime Support

• Process Inheritance: Updated the runner to use Stdio::inherit() for the child process. This allows the compiled Wave program to interact directly with the user's terminal for standard input/output.

4. Testing

• Integration Test: Updated test74.wave to demonstrate and verify the new input() functionality.

Example Usage

var age: i32;
var name: str;

// Reading basic types
input("Age: {}", &age);

// Reading into complex types (if supported by lvalue)
var scores: array<i32, 3> = [0, 0, 0];
input("Score: {}", &scores[0]);