style: clippy-1.93 machine-applicable auto-fixes (#967)

cargo clippy --fix on files the new clippy (1.93) flags: unused imports
(name_index, storyteller), manual_range_contains (block_irregularity),
length-comparison/is_empty (layer3, serialization). All behavior-preserving.
Surfaced because a warm target/ makes the pre-push hook actually run clippy
(it skips on cold worktrees). Remaining non-auto-fixable test-code lints
tracked in #967.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/src/atlas/block_irregularity.rs

@@ -110,7 +110,7 @@ mod tests {
         for a in &archetypes {
             let v = block_irregularity(300, a);
             assert!(
-                v >= 0.05 && v <= 1.0,
+                (0.05..=1.0).contains(&v),
                 "archetype {:?} gave {v} out of [0.05, 1.0]",
                 a
             );