[storage][vfs] Prepare for fuchsia.io transitions

These match statements are exhaustive, which break when we add
@transitional methods to fuchsia.io. This CL adds default cases to these
matches so that we add and remove @transitional methods.

Bug: 77623
Change-Id: I00ffa3334beb581791e8612bc5900256555e64e3
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/574555
API-Review: Adam Barth <abarth@google.com>
Commit-Queue: Adam Barth <abarth@google.com>
Reviewed-by: Tamir Duberstein <tamird@google.com>
Reviewed-by: Yifei Teng <yifeit@google.com>

Author: Adam Barth

src/lib/storage/vfs/rust/src/directory/connection/io1.rs

@@ -291,6 +291,7 @@ where
             DirectoryAdminRequest::Sync { responder } => {
                 responder.send(ZX_ERR_NOT_SUPPORTED)?;
             }
+            _ => {} // TODO(https://fxbug.dev/77623): Remove when the transition is complete.
         }
         Ok(ConnectionState::Alive)
     }

src/lib/storage/vfs/rust/src/file/connection/io1.rs

@@ -309,6 +309,7 @@ impl<T: 'static + File> FileConnection<T> {
                 fuchsia_trace::duration!("storage", "File::AdvisoryLock");
                 responder.send(&mut Err(ZX_ERR_NOT_SUPPORTED))?;
             }
+            _ => {} // TODO(https://fxbug.dev/77623): Remove when the transition is complete.
         }
         Ok(ConnectionState::Alive)
     }

src/lib/storage/vfs/rust/src/file/vmo/connection/io1.rs

@@ -459,6 +459,7 @@ impl VmoFileConnection {
             FileRequest::AdvisoryLock { request: _, responder } => {
                 responder.send(&mut Err(ZX_ERR_NOT_SUPPORTED))?;
             }
+            _ => {} // TODO(https://fxbug.dev/77623): Remove when the transition is complete.
         }
         Ok(ConnectionState::Alive)
     }