Add feature for unix systems that toggles sleep function used

[mayushiiii]

Description

Added a flag for changing the sleep function that is used on unix-based systems in order to increase efficiency.

What does this PR do?

As of right now, the z_sleep_ms function leads to an increased CPU usage, as it has multiple syscalls. The addition of the flag determines which sleep function is used depending on the user's needs. This will allow to decrease the CPU usage for systems where oversleep is not that big of a problem and is more acceptable than a high CPU usage.

Note: I'm sorry since I haven't done this before, but I'm not sure how to add a label to the PR. Seems to be a permission problem.

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🏷️ Label-Based Checklist

Based on the labels applied to this PR, please complete these additional requirements:

Labels: enhancement, good first issue

✨ Enhancement Requirements

Since this PR enhances existing functionality:

• Enhancement scope documented - Clear description of what is being improved
• Minimum necessary code - Implementation is as simple as possible, doesn't overcomplicate the system
• Backwards compatible - Existing code/APIs still work unchanged
• No new APIs added - Only improving existing functionality
• Tests updated - Existing tests pass, new test cases added if needed
• Performance improvement measured - If applicable, before/after metrics provided
• Documentation updated - Existing docs updated to reflect improvements
• User impact documented - How users benefit from this enhancement

Remember: Enhancements should not introduce new APIs or breaking changes.

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