Implement password storage for remote Jupyter servers

[Copilot]

This PR implements secure password storage for remote Jupyter servers, addressing a highly requested feature where users need to re-enter passwords every time they open VS Code.

Changes Made

Core Implementation

• Enhanced JupyterPasswordConnect to accept IEncryptedStorage dependency and implement password caching
• Added secure storage methods using VS Code's secrets API for password persistence
• Modified authentication flow to try stored passwords first, falling back to user prompts only when needed
• Implemented automatic cleanup of stored passwords when servers are removed

Authentication Flow

1. First connection: User enters password → authentication succeeds → password stored securely
2. Subsequent connections: Stored password retrieved automatically → seamless authentication
3. Authentication failure: Stored password cleared → user prompted for new password
4. Server removal: Associated passwords automatically deleted

Security & Storage

• Uses VS Code's secure extensionContext.secrets API for password storage
• Passwords stored with service name "jupyter-server-password"
• Unique storage keys based on server handles: "password-{server-handle}"
• Automatic password cleanup when servers are removed from the server list

Testing

• Updated existing unit tests to work with new constructor signature
• Added 2 new unit tests specifically for password storage functionality
• All 8 JupyterPasswordConnect tests passing
• Verified 1161 total unit tests still pass (no regressions)

User Experience

Before this change, users had to enter their password every time they opened VS Code or reconnected to a remote Jupyter server. Now passwords are securely stored and automatically retrieved, providing a seamless connection experience while maintaining security through VS Code's encrypted secrets storage.

The implementation preserves all existing behavior for backwards compatibility - users without stored passwords will continue to see the same prompts as before.

Fixes #13671.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• 0.0.0.123
  • Triggering command: node /home/REDACTED/work/vscode-jupyter/vscode-jupyter/node_modules/.bin/mocha --config ./build/.mocha.unittests.js.json ./out/interactive-window/generatedCodeStorageManager.unit.test.js ./out/interactive-window/shiftEnterBanner.unit.test.js ./out/kernels/helpers.unit.test.js ./out/kernels/kernelAutoReConnectMonitor.unit.test.js ./out/kernels/kernelAutoRestartMonitor.unit.test.js ./out/kernels/kernelCrashMonitor.unit.test.js ./out/kernels/kernelDependencyService.unit.test.js ./out/kernels/kernelFinder.unit.test.js ./out/kernels/kernelProvider.node.unit.test.js ./out/kernels/kernelProvider.web.unit.test.js ./out/kernels/kernelRefreshIndicator.node.unit.test.js ./out/kernels/kernelRefreshIndicator.web.unit.test.js ./out/test/package.nls.json.unit.test.js (packet block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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