Replace all assert! with debug_assert!

This results in a ~6% reduction in instruction count.

Cargo.toml

@@ -17,8 +17,11 @@ slice-group-by = "0.3.0"
 # Keep this in sync with libfuzzer_sys's crate version:
 arbitrary = { version = "^0.4.6", optional = true }
 
+# When testing regalloc2 by itself, enable debug assertions and overflow checks
 [profile.release]
 debug = true
+debug-assertions = true
+overflow-checks = true
 
 [features]
 default = []