tests: Add fuzzing harness for SigHasLowR(...) and ecdsa_signature_parse_der_lax(...)

src/pubkey.cpp

@@ -24,7 +24,7 @@ secp256k1_context* secp256k1_context_verify = nullptr;
  *  strict DER before being passed to this module, and we know it supports all
  *  violations present in the blockchain before that point.
  */
-static int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_signature* sig, const unsigned char *input, size_t inputlen) {
+int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_signature* sig, const unsigned char *input, size_t inputlen) {
     size_t rpos, rlen, spos, slen;
     size_t pos = 0;
     size_t lenbyte;