Minor code cleanup in check_system_module

[hoh]

Problem: Reading a file using f.open().read() keeps the file open until the garbage collector deletes the variable.

Since this uses Pathlib already, using Path(...).read_text() is cleaner and does not depend on the opening mode being r.

A file with no content could not be distinguished from a missing file. Instead, this changes the behaviour to return None when the file is missing instead of an empty string.

[github-actions]

The PR is categorized as 'BLUE' because the changes are relatively small and focused. The PR only includes a few lines of code changes (130 out of 130) and these changes are related to the is_command_available function and check_system_module function. The PR also includes a documentation update for the fix_message_validation function.

Highlighting:

• The is_command_available function now returns False when the command input is None, which is a small change but could potentially affect the behavior of the program.
• The check_system_module function now returns None when the system module does not exist, which is a small change but could potentially affect the behavior of the program.
• The fix_message_validation function now has a docstring describing its purpose and inputs, which is a small change but could potentially improve the readability of the code.

This PR is likely to have minimal impact on the codebase and is unlikely to introduce new bugs. It is recommended to review this PR as soon as possible to ensure that it does not introduce any unexpected behavior.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 57.92%. Comparing base (cc3f292) to head (164cd2e).

Files	Patch %	Lines
src/aleph/vm/utils.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #621   +/-   ##
=======================================
  Coverage   57.92%   57.92%           
=======================================
  Files          60       60           
  Lines        5402     5402           
  Branches      600      600           
=======================================
  Hits         3129     3129           
  Misses       2133     2133           
  Partials      140      140           

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[olethanh]

lgtm but I will let @nesitor have the final says on the behaviour change