Revert insta/similar opt-level — compilation overhead outweighs gains

The opt-level=3 for insta/similar adds recompilation time that exceeds
the snapshot diffing speedup. Plain debug builds with Rust vtt are
already the fastest configuration.

https://claude.ai/code/session_01MM41gBUbWHBiX8Skve91rG

Author: claude

Cargo.toml

@@ -167,13 +167,6 @@ ignored = [
 # and we don't rely on it for debugging that much.
 debug = false
 
-# Optimize snapshot testing dependencies in dev/test builds.
-# Snapshot diffing (insta + similar) is CPU-intensive; optimizing them
-# speeds up test runs without the compile-time cost of a full release build.
-[profile.dev.package]
-insta.opt-level = 3
-similar.opt-level = 3
-
 [profile.release]
 # Configurations explicitly listed here for clarity.
 # Using the best options for performance.