Issues #21521 and Fix applied to #21521

[Sheldon Kinney (PoorCameraQuality)]

Description

This improves the generic slicing failure message so users get a clearer hint when the failure may be related to supports and model placement (e.g. no room for supports after tight packing or Arrange All Models), as described in #21521.

Changes:

• plugins/CuraEngineBackend/CuraEngineBackend.py — extended the _slicing_error_message user-visible text (same @message context; existing crash-report / issue-tracker wording kept).
• resources/i18n/cura.pot — updated msgid for translators.

This improves user-facing diagnostics for a class of engine failures that previously only showed a generic "unexpected error" with no mention of supports or spacing.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Printer definition file(s)
• Translations

How Has This Been Tested?

• Manual / logical review — verified the string is valid Python, wrapped in catalog.i18nc("@message", ...), and that cura.pot matches the new source msgid.
• In-app slice failure path — recommend quickly triggering a known engine failure with supports enabled to confirm the message displays as expected.

Test Configuration:

• Operating System: Windows (change if you verified in-app on another OS)

Checklist:

• My code follows the style guidelines of this project as described in UltiMaker Meta and Cura QML best practices (string change only; no QML)
• I have read the Contribution guide
• I have commented my code, particularly in hard-to-understand areas (not needed for straightforward copy)
• I have uploaded any files required to test this change (issue When there's no room for supports to generate - unexpected error instead of descriptive cause #21521 links a repro .zip)

[github-actions]

Test Results

0 tests  ±0   0 ✅ ±0   0s ⏱️ ±0s
0 suites ±0   0 💤 ±0 
0 files   ±0   0 ❌ ±0 

Results for commit 1bd4fa2. ± Comparison against base commit 49c9926.