release: Bump extension version to 2026.10.0 (#26225)

## Summary
- Bump the extension from 2026.9.0-dev to the stable release candidate
2026.10.0.
- Update package-lock.json with version-only changes; dependencies are
unchanged.
- Retain the existing pet release/2026.12 reference as requested.

## Validation
- Verified package.json and both lockfile version fields agree on
2026.10.0.
- Compared parsed manifests against HEAD and confirmed no non-version
changes.
- git diff --check passed.

The pre-release pipeline may fail temporarily because this sets an even
stable version on main. After merging and creating release/2026.10,
restore main to 2026.11.0-dev before the next nightly pre-release.

Copilot-Session: 75f5808b-7a7d-4fd4-a1ee-b4ac8c340d36

Author: edvilme

package-lock.json

@@ -2,7 +2,7 @@
     "name": "python",
     "displayName": "Python",
     "description": "Python language support with extension access points for IntelliSense (Pylance), Debugging (Python Debugger), linting, formatting, refactoring, unit tests, and more.",
-    "version": "2026.9.0-dev",
+    "version": "2026.10.0",
     "featureFlags": {
         "usingNewInterpreterStorage": true
     },