Usage system: remove reserved usage for volumes

[olethanh]

of vm when calculate available disk space

Jira: ALEPH-420

This will help the scheduler scheduler more properly the available resource on CRN

Alternative approach to #780 as Sparse file were not properly created.

Explain what problem this PR is resolving

Related ClickUp, GitHub or Jira tickets : ALEPH-XXX

Self proofreading checklist

• The new code clear, easy to read and well commented.
• New code does not duplicate the functions of builtin or popular libraries.
• An LLM was used to review the new code and look for simplifications.
• New classes and functions contain docstrings explaining what they provide.
• All new code is covered by relevant tests.
• Documentation has been updated regarding these changes.
• Dependencies update in the project.toml have been mirrored in the Debian package build script packaging/Makefile

Changes

Explain the changes that were made. The idea is not to list exhaustively all the changes made (GitHub already provides a full diff), but to help the reviewers better understand:

• which specific file changes go together, e.g: when creating a table in the front-end, there usually is a config file that goes with it
• the reasoning behind some changes, e.g: deleted files because they are now redundant
• the behaviour to expect, e.g: tooltip has purple background color because the client likes it so, changed a key in the API response to be consistent with other endpoints

How to test

Explain how to test your PR.
If a specific config is required explain it here (account, data entry, ...)

Print screen / video

Upload here screenshots or videos showing the changes if relevant.

Notes

Things that the reviewers should know: known bugs that are out of the scope of the PR, other trade-offs that were made.
If the PR depends on a PR in another repo, or merges into another PR (i.o. main), it should also be mentioned here

[nesitor]

🚀

[codecov]

Codecov Report

Attention: Patch coverage is 41.66667% with 21 lines in your changes missing coverage. Please review.

Project coverage is 64.54%. Comparing base (db49c0e) to head (c7964cd).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/aleph/vm/controllers/firecracker/executable.py	16.66%	15 Missing ⚠️
src/aleph/vm/pool.py	53.84%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #784      +/-   ##
==========================================
- Coverage   64.75%   64.54%   -0.21%     
==========================================
  Files          78       78              
  Lines        7064     7083      +19     
  Branches      590      595       +5     
==========================================
- Hits         4574     4572       -2     
- Misses       2289     2309      +20     
- Partials      201      202       +1     

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