style: apply nightly rustfmt import grouping across the workspace

rustfmt.toml sets group_imports, imports_granularity and imports_layout,
which are nightly-only; agents formatted with stable rustfmt, which
ignored them. This is a formatting-only pass with `cargo +nightly fmt`.

Test Plan:
- cargo clippy --workspace --all-targets -- -D warnings
- cargo test --workspace

crates/ghostty-apprt-gtk/build.rs

@@ -3,9 +3,11 @@
 //! ZIG/src/apprt/gtk/build/{blueprint,gresource}.zig.
 
 #![allow(clippy::unwrap_used)]
-use std::fmt::Write as _;
-use std::path::{Path, PathBuf};
-use std::process::Command;
+use std::{
+    fmt::Write as _,
+    path::{Path, PathBuf},
+    process::Command,
+};
 
 const PREFIX: &str = "/com/mitchellh/ghostty";
 const APP_ID: &str = "com.mitchellh.ghostty";