feat: implement full 'for' loop support and strict type narrowing checks

[LunaStev]

This PR significantly enhances the Wave language by introducing full support for C-style for loops and enforcing stricter type safety across the board. Key improvements include a transition to a Result-based error reporting system in the parser and the prevention of unsafe implicit integer narrowing.

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Key Changes

1. Full for Loop Implementation

• Scoped Initialization: The for loop now supports local variable declarations within the initialization block (e.g., for (var i: i32 = 0; i < 10; i++)).
• Codegen & Scope: Implemented gen_for_ir in the LLVM backend with proper scope management. Variables declared in the loop header are automatically cleaned up when the loop exits.
• Validation: Added semantic passes to verify the integrity of loop headers, ensuring the condition is a boolean and the increment/initialization blocks are valid statements.

2. Strict Type Safety & Narrowing Prevention

• Forbidden Narrowing: Implicit narrowing of integers (e.g., assigning an i64 value to an i32 variable) is now a compiler error. This prevents subtle data loss bugs during assignments, binary operations, and function calls.
• Contextual Literal Inference: Numeric literals now use a "context-aware" inference strategy. Instead of defaulting to a fixed type, they look for type hints from the other side of an expression or the variable's declared type.

3. Parser Robustness & Error Reporting

• Result-based Parsing: Refactored the internal parser API from Option<T> to Result<T, ParseError>. This allows the compiler to provide detailed diagnostic messages, including source labels, line numbers, and "help" hints.
• Improved Imports: The import system now propagates structured errors, making it much easier to debug syntax errors within imported standard library modules.

4. Standard Library & Optimization

• Module Refactor: Reorganized the standard library into role-based modules (e.g., moving from umbrella files to specific paths like std::time::clock).
• Optimization Normalization: Normalized the backend optimization pipeline. The -Ofast flag now correctly maps to -O3 logic, and all flags are consistently applied through the new LLVM PassBuilder.

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Example Usage

Standard for loop with local scope:

fun main() {
    // i is only visible inside the loop
    for (var i: i32 = 0; i < 5; i++) {
        println("Iteration: {}", i);
    }
}

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Benefits

• Expressiveness: Standard for loops provide a more ergonomic way to handle iterations compared to while loops.
• Safety: Stricter type checks catch potential overflow or data loss issues at compile-time.
• Diagnostic Quality: The shift to Result-based parsing provides a much better developer experience through clearer error messages.