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-renderer/src/options.rs

@@ -3,8 +3,7 @@ use std::sync::Arc;
 
 use ghostty_font::SharedGrid;
 
-use crate::generic::Host;
-use crate::size::Size;
+use crate::{generic::Host, size::Size};
 
 /// Options for constructing a renderer.
 ///