fix: Remove proving key buf len estimation (#26)

remove proving key buf len estimation, generalize like init_verification_key in standard_example

barretenberg/src/aztec/rollup/proofs/standard_example/standard_example.cpp

@@ -178,20 +178,12 @@ size_t c_init_proving_key(uint8_t const* constraint_system_buf, uint8_t const**
     auto composer = create_circuit(constraint_system, std::move(crs_factory));
     auto proving_key = composer.compute_proving_key();
 
-    // Computing the size of the serialized key is non trivial. We know it's ~331mb.
-    // Allocate a buffer large enough to hold it, and abort if we overflow.
-    // This is to keep memory usage down.
-    size_t total_buf_len = 350 * 1024 * 1024;
-    auto raw_buf = (uint8_t*)malloc(total_buf_len);
-    auto raw_buf_end = raw_buf;
-    write(raw_buf_end, *proving_key);
+    auto buffer = to_buffer(*proving_key);
+    auto raw_buf = (uint8_t*)malloc(buffer.size());
+    memcpy(raw_buf, (void*)buffer.data(), buffer.size());
     *pk_buf = raw_buf;
-    auto len = static_cast<uint32_t>(raw_buf_end - raw_buf);
-    if (len > total_buf_len) {
-        info("Buffer overflow serializing proving key.");
-        std::abort();
-    }
-    return len;
+
+    return buffer.size();
 }
 
 size_t c_init_verification_key(void* pippenger, uint8_t const* g2x, uint8_t const* pk_buf, uint8_t const** vk_buf)