Removed implicit singleton behavior of Tolerance.

[chenkasirer]

Closes #1509

• Removed Singleton behavior of Tolerance which was leading to accidental global state modification.
• Tolerance(...) now creates independent instances of Tolerance
• Added Tolerance.update() to update an instance in-place (e.g. TOL)
• Added Tolerance.temporary() context manager for local modifications of tolerance.

What type of change is this?

• Bug fix in a backwards-compatible manner.
• New feature in a backwards-compatible manner.
• Breaking change: bug fix or new feature that involve incompatible API changes.
• Other (e.g. doc update, configuration, etc)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I added a line to the CHANGELOG.md file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• I ran all tests on my computer and it's all green (i.e. invoke test).
• I ran lint on my computer and there are no errors (i.e. invoke lint).
• I added new functions/classes and made them available on a second-level import, e.g. compas.datastructures.Mesh.
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.30%. Comparing base (e34268a) to head (a8f0ad6).

Files with missing lines	Patch %	Lines
src/compas/tolerance.py	81.81%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1510      +/-   ##
==========================================
+ Coverage   62.26%   62.30%   +0.04%     
==========================================
  Files         208      208              
  Lines       22452    22475      +23     
==========================================
+ Hits        13979    14003      +24     
+ Misses       8473     8472       -1     

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[Copilot]

Pull request overview

This PR removes the implicit singleton behavior of Tolerance, so Tolerance(...) now returns independent instances while TOL remains the explicit global instance. It also introduces explicit APIs for mutating global tolerance state (TOL.update and TOL.temporary) and documents these behaviors, plus updates the changelog and tests accordingly.

Changes:

• Refactored compas.tolerance.Tolerance to be a regular class (no singleton), while keeping a module-level TOL = Tolerance() as the shared global instance.
• Added Tolerance.update(...) and Tolerance.temporary(...) to support explicit, scoped modifications of tolerance settings, and updated module/class docstrings.
• Extended tests/compas/test_tolerance.py and CHANGELOG.md to cover and document the new behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/compas/tolerance.py	Removes singleton machinery, adds explicit mutation helpers (update, temporary), extends documentation, and keeps TOL as a dedicated global instance.
tests/compas/test_tolerance.py	Adds tests to verify independent Tolerance instances, explicit TOL.update, and scoped TOL.temporary behavior (including restoration on exceptions).
CHANGELOG.md	Documents the new TOL.update/TOL.temporary APIs and the change away from the singleton Tolerance pattern.

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[Copilot]

temporary() saves and restores self._unit, but updates the unit via self.update(unit=...), which assigns to self.unit (a plain instance attribute, since there is no unit property). As a result, using TOL.temporary(unit=...) will change TOL.unit permanently instead of reverting it on context exit, unlike the other fields that correctly round-trip via their private attributes. To make the context manager behave consistently and avoid accidental global state changes for unit, the implementation should either snapshot and restore self.unit (not self._unit) or introduce a proper unit property that proxies to _unit and make both update and temporary use that.