Improve performance on path manipulation nodes

[Alxiice]

Description

• Add a node GetFileExtension
• Replace desc.Node by desc.CommandLineNode on
  • GetParentFolder
  • FlattenFiles
  • PathJoin

Using CommandLineNode bypass the _processInIsolatedEnvironment call (see #3166) that launches a subprocess.
Bypassing it saves several seconds: the node compute takes almost 0 sec.

[gemini-code-assist]

Code Review

This pull request refactors several utility nodes (FlattenFiles, GetParentFolder, and PathJoin) to inherit from desc.CommandLineNode instead of desc.Node, transitioning their execution logic from process to processChunk. It also introduces a new GetFileExtension node. The feedback suggests adding a defensive check in the new GetFileExtension node to prevent a potential TypeError if the input path is empty or None.

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[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.07%. Comparing base (1d89d80) to head (17cafa3).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
meshroom/core/desc/node.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3167      +/-   ##
===========================================
- Coverage    86.07%   86.07%   -0.01%     
===========================================
  Files           78       78              
  Lines        12111    12115       +4     
===========================================
+ Hits         10425    10428       +3     
- Misses        1686     1687       +1     

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[fabiencastan]

Do not use commandlinenode for that. This is hack. Add a way to disable subprocess in Node.

[Alxiice]

@fabiencastan I added a InlineNode type (we can discuss about the name). I found that was a simpler way to avoid computing inside the current env (rather than modifying the whole graph compute / process system).