Allow the bench profile to compile faster

There we don't necessarily need every last bit of optimization like
one would want in release profiles, but build performance is of the essence
for developer productivity.

Cargo.toml

@@ -90,3 +90,8 @@ codegen-units = 1 # Compile crates one after another so the compiler can optimiz
 lto = true        # Enables link to optimizations
 opt-level = "s"   # Optimize for binary size
 debug = true      # Enable debug symbols, for profiling
+
+[profile.bench]
+codegen-units = 256
+lto = false
+opt-level = 3