[Bug]: Fix relative audio file paths, timing logic, and requirements in Exercise-Timer

[Prayas340]

Description

The Exercise-Timer script has a few bugs and limitations:

1. Audio Path Issue: Running exercise_cli.py from outside the Exercise-Timer directory crashes with FileNotFoundError because audio paths are hardcoded as relative strings.
2. Double Rest Interval: The interval sleep executes both before and after each rep, causing double rest duration between sets and an unnecessary rest delay after the final rep.
3. Invalid Dependency: ime (a Python standard library module) is listed in
   equirements.txt.
4. Lack of Input Validation & Terminal Feedback: Options accept negative numbers or 0, and there is no live visual countdown during workouts.

Type of issue

• Feature (New Script)
• Bug
• Documentation

Checklist:

• I have read the project guidelines.
• I have checked previous issues to avoid duplicates.
• This issue will be meaningful for the project.
• I have proposed a possible solution for the bug