toolchain: Respect currently focused file when querying toolchains (#28875)

Closes #21743


https://github.com/user-attachments/assets/0230f233-58a4-494c-90af-28ce82f9fc1d


Release Notes:

- Virtual environment picker now looks up virtual environment based on
parent directory of active file; this enables having multiple active
virtual environments in a single worktree.

crates/project/src/toolchain_store.rs

@@ -55,6 +55,7 @@ impl ToolchainStore {
         });
         Self(ToolchainStoreInner::Local(entity, subscription))
     }
+
     pub(super) fn remote(project_id: u64, client: AnyProtoClient, cx: &mut App) -> Self {
         Self(ToolchainStoreInner::Remote(
             cx.new(|_| RemoteToolchainStore { client, project_id }),
@@ -285,7 +286,7 @@ struct LocalStore(WeakEntity<LocalToolchainStore>);
 struct RemoteStore(WeakEntity<RemoteToolchainStore>);
 
 #[derive(Clone)]
-pub(crate) enum ToolchainStoreEvent {
+pub enum ToolchainStoreEvent {
     ToolchainActivated,
 }