[core] use callable instead of checking for FunctionType instance type

[fabiencastan]

This pull request updates several places in the codebase to use the more general callable() function instead of checking specifically for types.FunctionType. This change improves compatibility and flexibility when determining if an object can be called like a function.

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.55%. Comparing base (0438f49) to head (1bd0f3d).
⚠️ Report is 3 commits behind head on develop.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
meshroom/core/attribute.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2900      +/-   ##
===========================================
- Coverage    79.56%   79.55%   -0.01%     
===========================================
  Files           51       51              
  Lines         6977     6974       -3     
===========================================
- Hits          5551     5548       -3     
  Misses        1426     1426              

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[Copilot]

Pull Request Overview

This pull request replaces direct types.FunctionType instance checks with the more general callable() function across the Meshroom codebase. This change improves type checking flexibility by accommodating any callable object, not just function types.

• Replaces isinstance(obj, types.FunctionType) with callable(obj) in multiple locations
• Improves compatibility with callable objects like lambdas, methods, and classes with __call__
• Maintains the same logical behavior while being more inclusive of callable types

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
meshroom/core/node.py	Updates attribute group callable check in command variable building
meshroom/core/desc/attribute.py	Updates expression detection logic to use callable()
meshroom/core/attribute.py	Updates multiple callable checks for value setting, default values, validation, and enabled state

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