[EXTERNAL] Fix invalid use statement in example code modify_letter

[BenaliOssama]

CON-#### | [EXTERNAL] Fix invalid use statement in example code

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Why?

The Rust example code provided in the Usage section includes the following line:

use modify_letter::*modify_letter*;

This is invalid Rust syntax and causes a compile-time error.

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Solution Overview

This pull request corrects the invalid use statement. The line:

use modify_letter::*modify_letter*;

was replaced with:

use modify_letter::*;

This version is valid and compiles correctly, allowing students to test the functions as intended.

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Implementation Details

Only the import line was changed. No other logic or structure was modified.

Other approaches (like importing specific functions) were considered, but using use modify_letter::*; keeps the example simpler and matches the original intent of showing all functions in use.

[pedrodesu]

That was exactly our intention - A minor mistake I've overlooked. Thank you so much for your contribution @BenaliOssama! Merging.