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-config/src/io.rs

@@ -1,10 +1,13 @@
 //! Readable IO config values (port of `config/io.zig`).
 
-use crate::cli_args::{ArgError, ConfigField, split_tagged_union};
-use crate::formatter::EntryFormatter;
-use crate::string;
 use std::fmt;
 
+use crate::{
+    cli_args::{ArgError, ConfigField, split_tagged_union},
+    formatter::EntryFormatter,
+    string,
+};
+
 /// ReadableIO is some kind of IO source that is readable.
 ///
 /// It can be either a direct string or a filepath. The filepath will