Basic execution elements and basic skr_app calls

[Alexiscomete]

• u32 type only
• column in tokens
• error display (base) and hints
• create a variable
• edit a variable
• do basic calculations with u32
• print variable (with or without a new line)
• get user input
• assert that two values are equal

[Copilot]

Pull Request Overview

This PR adds core execution support for the SKR language, introduces a CharsIterator to track token positions, and implements native calls (print, println, read_int, assert_eq) with detailed error handling and hints.

• Refactor tokenizer to CharsIterator carrying line/column information
• Implement ExecutionContext, AST Evaluate/Execute traits, and native calls
• Update all GraphDisplay impls to include indentation for clearer flowcharts

Reviewed Changes

Copilot reviewed 22 out of 23 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test1, test2, test3	Added flowchart outputs for basic calculations and variable ops
test.skrb	Updated example script to use new syntax and demonstrate calls
src/utils.rs	Enhanced cross‐platform clear using ANSI codes and improved doc
src/tokens.rs	Refactored tokenizer to use CharsIterator for line/column info
src/execute.rs	Built ExecutionContext, variable scopes, native call handling
src/parse/nodes/*	Added Evaluate/Execute impls and updated GraphDisplay APIs
src/main.rs	Improved CLI flow, --show-ast, colored output, error handling
README.md	Markdown formatting fix
Cargo.toml	Added colored dependency

Comments suppressed due to low confidence (1)

src/execute.rs:5

• [nitpick] Aliasing primitives as OperationI/OperationO can be confusing; consider using more descriptive names such as EvalInput/EvalResult or Value/Result to clarify their roles.

pub type OperationI = u32;