Merge util file into utils folder

[gselzer]

Closes #91.

The functions that previously existed in scenex.util have been moved to either scenex.util._app or scenex.util._tree. The way things got partitioned out, all of the functions moved to scenex.util._app are still exported by the toplevel scenex module. We could also make scenex.util._app public at some point if there's reason to do so.

@tlambert03 note that as a part of this, I've made your tree_repr and tree_dict functions private. I think that's fine, they're more debugging tools than API that should be depended on - let me know if you disagree

[gselzer]

Alternatively, tree_repr and tree_dict could just go into scenex.model._nodes/node.

[Copilot]

Pull request overview

This PR consolidates the former scenex.util helpers into the scenex.utils package, splitting app-related utilities into scenex.utils._app and tree/debug helpers into scenex.utils._tree, and updates internal imports/tests accordingly.

Changes:

• Added scenex.utils._tree with tree_repr/tree_dict and removed the same logic from the app utilities module.
• Updated exports so scenex.utils exposes app-level helpers (show, run, etc.) and scenex top-level imports those from scenex.utils._app.
• Updated tests and Node.tree_repr() to use the new locations.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/test_basic_scene.py	Updates tests to call tree helpers from the new location (currently needs an explicit import of the _tree submodule).
src/scenex/utils/_tree.py	New module containing tree debugging utilities (contains a leaf-detection bug for generator-like children).
src/scenex/utils/_app.py	Removes tree utilities and focuses on application/canvas helpers; updates a backend registry import.
src/scenex/utils/init.py	Re-exports app helpers from _app as the scenex.utils public surface.
src/scenex/model/_nodes/node.py	Updates Node.tree_repr() to import tree_repr from scenex.utils._tree.
src/scenex/init.py	Updates top-level exports to import app helpers from scenex.utils._app (breaking change for import scenex.util consumers unless shimmed).

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[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.13%. Comparing base (c719690) to head (0303c95).

Files with missing lines	Patch %	Lines
src/scenex/utils/_tree.py	82.85%	6 Missing ⚠️
src/scenex/model/_nodes/node.py	0.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (83.33%) is below the target coverage (85.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #92   +/-   ##
=======================================
  Coverage   88.12%   88.13%           
=======================================
  Files          64       65    +1     
  Lines        3309     3311    +2     
=======================================
+ Hits         2916     2918    +2     
  Misses        393      393           

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