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/repeatable_string_map.rs

@@ -2,10 +2,13 @@
 //! string map. This isn't called "StringMap" because I find that sometimes
 //! leads to confusion that it _accepts_ a map such as JSON dict.
 
-use crate::cli_args::{ArgError, ConfigField};
-use crate::formatter::EntryFormatter;
 use std::fmt;
 
+use crate::{
+    cli_args::{ArgError, ConfigField},
+    formatter::EntryFormatter,
+};
+
 /// std.ascii.whitespace
 fn is_ascii_ws(c: char) -> bool {
     matches!(c, ' ' | '\t' | '\n' | '\r' | '\x0b' | '\x0c')