style: rustfmt the blob-removal code (fix the CI fmt gate)

The blob-removal commit (6b4c4dc) failed CI's fmt gate — long assert! lines
and a doc comment that stock rustfmt wraps. No behaviour change; just
`cargo fmt`. Verified via `nix develop -c cargo fmt --check`.

tests/e2e_pty.rs

@@ -437,7 +437,11 @@ fn opens_a_legacy_v1_blob_project_by_migrating_to_text() {
         ),
     )
     .expect("write project.yaml");
-    fs::write(proj.join("data").join("Files.csv"), "id,payload\n1,aGVsbG8=\n").expect("write csv");
+    fs::write(
+        proj.join("data").join("Files.csv"),
+        "id,payload\n1,aGVsbG8=\n",
+    )
+    .expect("write csv");
     fs::write(root.join("last_project"), format!("{}\n", proj.display())).expect("write resume");
 
     // Open via --resume: the runtime migrates blob→text and rebuilds, so