Jailer tweaks

[ShadowCurse]

Changes

• Clarify the reason for main function wrapping. This is mainly because I have this question each time I look at this code and each time need to discover the reason again.
• Use Rust feature to create CStr constants for paths avoiding runtime conversion.

Reason

Since Rust 1.77 CStr can be created with c prefix to string. Use this to simplify the code and remove runtime conversions.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.

PR Checklist

• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkstyle to verify that the PR passes the
  automated style checks.
• I have described what is done in these changes, why they are needed, and
  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
• I have mentioned all user-facing changes in CHANGELOG.md.
• If a specific issue led to this PR, this PR closes the issue.
• When making API changes, I have followed the
  Runbook for Firecracker API changes.
• I have tested all new and changed functionalities in unit tests and/or
  integration tests.
• I have linked an issue to every new TODO.

---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

Attention: Patch coverage is 18.75000% with 13 lines in your changes missing coverage. Please review.

Project coverage is 83.19%. Comparing base (74a5161) to head (5544bd1).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/jailer/src/chroot.rs	0.00%	10 Missing ⚠️
src/jailer/src/env.rs	50.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5068   +/-   ##
=======================================
  Coverage   83.19%   83.19%           
=======================================
  Files         247      247           
  Lines       26641    26638    -3     
=======================================
- Hits        22163    22162    -1     
+ Misses       4478     4476    -2     

Flag	Coverage Δ
5.10-c5n.metal	83.67% <18.75%> (+<0.01%)	⬆️
5.10-m5n.metal	83.66% <18.75%> (+<0.01%)	⬆️
5.10-m6a.metal	82.87% <18.75%> (+0.01%)	⬆️
5.10-m6g.metal	79.67% <18.75%> (+<0.01%)	⬆️
5.10-m6i.metal	83.65% <18.75%> (+<0.01%)	⬆️
5.10-m7g.metal	79.67% <18.75%> (+<0.01%)	⬆️
6.1-c5n.metal	83.67% <18.75%> (+<0.01%)	⬆️
6.1-m5n.metal	83.66% <18.75%> (+<0.01%)	⬆️
6.1-m6a.metal	82.87% <18.75%> (+<0.01%)	⬆️
6.1-m6g.metal	79.67% <18.75%> (+<0.01%)	⬆️
6.1-m6i.metal	83.65% <18.75%> (+<0.01%)	⬆️
6.1-m7g.metal	79.67% <18.75%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[roypat]

Nice!