refactor: remove TLS from vcpus

[ShadowCurse]

Changes

Instead of storing mmaped kvm_vcpu struct in the TLS, we can have it in the VcpuHandle. This way we don't need to deal with TLS and it's synchronization.

Reason

Dealing with TLS was difficult and bug prone

License Acceptance

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PR Checklist

• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkbuild --all to verify that the PR passes
  build checks on all supported architectures.
• 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.
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---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

❌ Patch coverage is 70.96774% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.68%. Comparing base (f90a95b) to head (e46eba1).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/vmm/src/builder.rs	0.00%	8 Missing ⚠️
src/vmm/src/lib.rs	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5428      +/-   ##
==========================================
- Coverage   82.68%   82.68%   -0.01%     
==========================================
  Files         263      263              
  Lines       27473    27478       +5     
==========================================
+ Hits        22717    22719       +2     
- Misses       4756     4759       +3     

Flag	Coverage Δ
5.10-m5n.metal	82.85% <70.96%> (+<0.01%)	⬆️
5.10-m6a.metal	82.10% <70.96%> (+<0.01%)	⬆️
5.10-m6g.metal	79.46% <70.96%> (-0.01%)	⬇️
5.10-m6i.metal	82.84% <70.96%> (+<0.01%)	⬆️
5.10-m7a.metal-48xl	82.09% <70.96%> (+<0.01%)	⬆️
5.10-m7g.metal	79.47% <70.96%> (-0.01%)	⬇️
5.10-m7i.metal-24xl	82.82% <70.96%> (+<0.01%)	⬆️
5.10-m7i.metal-48xl	82.82% <70.96%> (-0.01%)	⬇️
5.10-m8g.metal-24xl	79.46% <70.96%> (-0.01%)	⬇️
5.10-m8g.metal-48xl	79.46% <70.96%> (-0.01%)	⬇️
6.1-m5n.metal	82.89% <70.96%> (+<0.01%)	⬆️
6.1-m6a.metal	82.14% <70.96%> (+<0.01%)	⬆️
6.1-m6g.metal	79.46% <70.96%> (-0.01%)	⬇️
6.1-m6i.metal	82.88% <70.96%> (-0.01%)	⬇️
6.1-m7a.metal-48xl	82.13% <70.96%> (-0.01%)	⬇️
6.1-m7g.metal	79.46% <70.96%> (-0.01%)	⬇️
6.1-m7i.metal-24xl	82.89% <70.96%> (-0.01%)	⬇️
6.1-m7i.metal-48xl	82.89% <70.96%> (-0.01%)	⬇️
6.1-m8g.metal-24xl	79.46% <70.96%> (-0.01%)	⬇️
6.1-m8g.metal-48xl	79.46% <70.96%> (-0.01%)	⬇️

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