oss-fuzz: allow switching between "dev" and "release" mode easily

Mostly to be able to experiment with the fuzz target by injecting
trivial bugs catchable by ASan to make sure that they aren't
compiled out.

It should help to track down weird issues like
google/oss-fuzz#5865 (comment)

fuzz/oss-fuzz.sh

@@ -2,7 +2,14 @@
 
 set -eux
 
-cargo fuzz build -O --verbose
-cp fuzz/target/x86_64-unknown-linux-gnu/release/fuzz_from_to_string $OUT/fuzz_from_to_string
+build_type=${1:-"release"}
+build_args="--release"
+if [[ "$build_type" =~ "dev" ]]; then
+ build_type="debug"
+ build_args="--dev"
+fi
+
+cargo fuzz build $build_args --verbose
+cp "fuzz/target/x86_64-unknown-linux-gnu/$build_type/fuzz_from_to_string" $OUT/fuzz_from_to_string
 wget https://raw.githubusercontent.com/google/fuzzing/master/dictionaries/toml.dict -O $OUT/fuzz_from_to_string.dict
 zip -r $OUT/fuzz_from_to_string_seed_corpus.zip test-suite/tests