Remove unwrap in PIO device manager setup TODO

[DakshinD]

Changes

Replaced unwraps with map_err to propagate LegacyDeviceError as VmmError::LegacyIOBus to prevent potential panics.

Reason

Resolves TODO Remove these unwraps. see #3273

License Acceptance

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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

All modified and coverable lines are covered by tests ✅

Project coverage is 83.10%. Comparing base (a6d0d93) to head (bf3b182).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5138      +/-   ##
==========================================
+ Coverage   83.02%   83.10%   +0.07%     
==========================================
  Files         250      250              
  Lines       26902    26900       -2     
==========================================
+ Hits        22335    22354      +19     
+ Misses       4567     4546      -21     

Flag	Coverage Δ
5.10-c5n.metal	83.59% <100.00%> (+0.03%)	⬆️
5.10-m5n.metal	83.59% <100.00%> (+0.03%)	⬆️
5.10-m6a.metal	82.82% <100.00%> (+0.03%)	⬆️
5.10-m6g.metal	79.38% <0.00%> (+0.01%)	⬆️
5.10-m6i.metal	83.59% <100.00%> (+0.03%)	⬆️
5.10-m7a.metal-48xl	82.80% <100.00%> (?)
5.10-m7g.metal	79.38% <0.00%> (+0.01%)	⬆️
5.10-m7i.metal-24xl	83.54% <100.00%> (?)
5.10-m7i.metal-48xl	83.55% <100.00%> (?)
6.1-c5n.metal	83.63% <100.00%> (+0.02%)	⬆️
6.1-m5n.metal	83.64% <100.00%> (+0.03%)	⬆️
6.1-m6a.metal	82.86% <100.00%> (+0.03%)	⬆️
6.1-m6g.metal	79.38% <0.00%> (+0.01%)	⬆️
6.1-m6i.metal	83.63% <100.00%> (+0.02%)	⬆️
6.1-m7a.metal-48xl	82.85% <100.00%> (?)
6.1-m7g.metal	79.38% <0.00%> (+0.02%)	⬆️
6.1-m7i.metal-24xl	83.64% <100.00%> (?)
6.1-m7i.metal-48xl	83.64% <100.00%> (?)

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[DakshinD]

Saw that my commit message was failing checkstyle test. Just amended that and force pushed it over.

[roypat]

Thanks!