[yuefdev]

Description

Query diagnostics only for visible documents, once per URI even in split editors. Error counting, fixed-error credit and mood changes keep their existing behaviour.

Fixes #26.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• node --test: passed. The regression drives the extension's diagnostics callback and checks query scope, split-editor deduplication, error credit and an empty editor list.
• node --check extension.js: passed.
• Manual test in VS Code Extension Development Host
• Verified SVG renders correctly (not applicable)

Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation (CHANGELOG.md).
• My changes generate no new warnings/errors in the console (not checked in a live host).

No test or lint scripts are defined in package.json; the regression uses Node's built-in test runner.

[Adnan9-63]

LGTM! Fantastic work @yuefdev 🚀

Everything looks super clean. Thanks for fixing this performance bottleneck and updating the CHANGELOG! Merging now.