[#488] waitset attachment id improvements

[elfenpiff]

Notes for Reviewer

To be able to perform better debugging, the streaming operator for the waitset attachment id was added. Furthermore, std::hash was implemented for it to be able to organize it in a hash map.

Pre-Review Checklist for the PR Author

1. Add sensible notes for the reviewer
2. PR title is short, expressive and meaningful
3. Relevant issues are linked in the References section
4. Every source code file has a copyright header with SPDX-License-Identifier: Apache-2.0 OR MIT
5. Branch follows the naming format (iox2-123-introduce-posix-ipc-example)
6. Commits messages are according to this guideline
   • Commit messages have the issue ID ([#123] Add posix ipc example)
   • Commit author matches Eclipse Contributor Agreement (and ECA is signed)
7. Tests follow the best practice for testing
8. Changelog updated in the unreleased section including API breaking changes
9. Assign PR to reviewer
10. All checks have passed (except task-list-completed)

Checklist for the PR Reviewer

• Commits are properly organized and messages are according to the guideline
• Unit tests have been written for new behavior
• Public API is documented
• PR title describes the changes

Post-review Checklist for the PR Author

1. All open points are addressed and tracked via issues

References

Closes #488

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 79.13%. Comparing base (5f6a0dc) to head (355b962).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
iceoryx2/src/port/waitset.rs	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #489      +/-   ##
==========================================
- Coverage   79.19%   79.13%   -0.06%     
==========================================
  Files         200      200              
  Lines       23716    23724       +8     
==========================================
- Hits        18781    18775       -6     
- Misses       4935     4949      +14     

Files with missing lines	Coverage Δ
iceoryx2/src/port/waitset.rs	75.68% <0.00%> (-1.89%)	⬇️

... and 6 files with indirect coverage changes

[elBoberido]

nitpik

Suggested change

	std::string empty(len, '\0');
	std::string hash(len, '\0');