[core] Refactoring variable management and expression evaluation for performances

[fabiencastan]

cmdVars has been splitted between: expVars, staticExpVars and cmdLineVars.

• Command line vars are now only computed during the command line
  generation for the "CommandLineNode".
• internalFolder is now initialized in the BaseNode, instead of Node
  (even if there is the particular case of "InputNode" which does not need
  it). And its value is computed once in the updateInternals instead of
  redoing the string format again and again.
• internalFolder is not serialized/deserialized anymore as it is a
  static information. At the beginning, it was designed to be customized
  per node, but this flexibility/complexity seems useless as it has never
  been used over many years. We now use "{nodeCacheFolder}" directly.

[Copilot]

Pull Request Overview

This PR refactors variable management and expression evaluation to improve performance by separating expression variables from command line variables and optimizing internal folder path computations.

• Separated expression evaluation (_expVars) from command line generation (createCmdLineVars())
• Optimized internal folder path computation by removing redundant cache directory joins
• Added static expression variables for commonly used values like nodeType and nodeSourceCodeFolder

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
meshroom/core/node.py	Core refactoring separating expression variables from command line generation, optimizing path computations
meshroom/core/desc/node.py	Updated command line building to use new variable separation approach
meshroom/core/attribute.py	Updated to use new expression variables and added error handling for malformed expressions
tests/test_nodeCommandLineFormatting.py	Updated test assertions to use new _expVars instead of _cmdVars

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[codecov]

Codecov Report

❌ Patch coverage is 64.28571% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.06%. Comparing base (aabe589) to head (c95c257).
⚠️ Report is 21 commits behind head on develop.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
meshroom/core/node.py	55.35%	25 Missing ⚠️
meshroom/core/attribute.py	57.14%	3 Missing ⚠️
meshroom/core/desc/node.py	0.00%	2 Missing ⚠️

❌ Your patch status has failed because the patch coverage (64.28%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2888      +/-   ##
===========================================
- Coverage    79.41%   79.06%   -0.36%     
===========================================
  Files           51       51              
  Lines         6987     7007      +20     
===========================================
- Hits          5549     5540       -9     
- Misses        1438     1467      +29     

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