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/src/gl.rs

@@ -7,8 +7,7 @@
 //! `glow::Context::from_loader_function` need. Call it only while the GLArea
 //! context is current.
 
-use std::ffi::c_void;
-use std::sync::OnceLock;
+use std::{ffi::c_void, sync::OnceLock};
 
 fn epoxy() -> Option<&'static libloading::Library> {
     static LIB: OnceLock<Option<libloading::Library>> = OnceLock::new();