Review the unsafe fn (1st round).

[evshary]

Description

The PR is the 1st round review dealing with #1684.
We wanted to make sure

1. Don't use unsafe fn if we can avoid the UB inside the function
2. Every unsafe fn should include /// # Safety
3. Enable unsafe_op_in_unsafe_fn, which will be enabled by default in Edition 2024
4. Having // SAFETY before an unsafe block.

What does this PR do?

Fix the unsafe fn usage inside Zenoh

Why is this change needed?

Ensure that we are using unsafe correctly.

Related Issues

#1684

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🏷️ Label-Based Checklist

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

Labels: enhancement

✨ 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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[codecov]

Codecov Report

❌ Patch coverage is 40.00000% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.99%. Comparing base (b3b5161) to head (4f80769).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
commons/zenoh-util/src/ffi/mod.rs	0.00%	10 Missing ⚠️
commons/zenoh-util/src/lib_loader.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2396      +/-   ##
==========================================
+ Coverage   71.95%   71.99%   +0.04%     
==========================================
  Files         390      390              
  Lines       62786    62790       +4     
==========================================
+ Hits        45176    45208      +32     
+ Misses      17610    17582      -28     

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