Refresh environment managers automatically when expanding tree node (#783)

When expanding environment manager nodes in the Environment Managers
view, newly created environments (such as those created by `pipenv
install pytest` or `conda create -n myenv`) were not appearing until the
user manually refreshed the view.

This change adds automatic refresh functionality for all environment
managers when their tree node is expanded. The implementation:

- Calls the existing `manager.refresh(undefined)` method before
retrieving environments for any manager type
- Affects all environment managers (Pipenv, Conda, Venv, Poetry, etc.)
providing consistent behavior
- Uses the established refresh mechanism that properly updates
collections and fires change events

**Before:**
1. Run `pipenv install pytest` or create a new environment with any
manager
2. Open Environment Managers view
3. Expand environment manager node
4. New environment is not visible until manual refresh

**After:**
1. Run `pipenv install pytest` or create a new environment with any
manager
2. Open Environment Managers view  
3. Expand environment manager node
4. New environment appears immediately

The fix is minimal and targeted, modifying only 1 line of code in the
`getChildren` method in `EnvManagerView`. Unit tests have been updated
to validate the core logic for any manager type.

Fixes #782.

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: eleanorjboyd <[email protected]>

Author: Copilot

src/features/views/envManagersView.ts

@@ -95,6 +95,10 @@ export class EnvManagerView implements TreeDataProvider<EnvTreeItem>, Disposable
         if (element.kind === EnvTreeItemKind.manager) {
             const manager = (element as EnvManagerTreeItem).manager;
             const views: EnvTreeItem[] = [];
+            
+            // Refresh manager when expanded to pick up newly created environments
+            await manager.refresh(undefined);
+            
             const envs = await manager.getEnvironments('all');
             envs.filter((e) => !e.group).forEach((env) => {
                 const view = new PythonEnvTreeItem(env, element as EnvManagerTreeItem, this.selected.get(env.envId.id));