Correctly handle fetch JSON numbers in Java and C++ drivers (#603)

## Usage and product changes

When receiving the fetch response across the FFI boundary as JSON, Java
and C++ drivers would incorrectly parse numbers: Java as a single
precision float, and C++ as an integer. This PR fixes both those issues.

## Implementation

Fixes #601

Author: dmitrii-ubskii

cpp/lib/answer/json.cpp

@@ -287,7 +287,7 @@ JSON JSONBuilder::build(const nlohmann::json& from) {
         case nlohmann::json::value_t::number_unsigned:
             return JSON((JSONLong)from.get<unsigned>());
         case nlohmann::json::value_t::number_float:
-            return JSON((JSONDouble)from.get<unsigned>());
+            return JSON((JSONDouble)from.get<double>());
         case nlohmann::json::value_t::string:
             return JSON(from.get<std::string>());
 

java/api/answer/JSON.java

@@ -51,7 +51,7 @@ private static JSON of(JsonValue value) {
         } else if (value.isString()) {
             return new JSON.String(value.asString());
         } else if (value.isNumber()) {
-            return new JSON.Number(value.asFloat());
+            return new JSON.Number(value.asDouble());
         } else if (value.isBoolean()) {
             return new JSON.Boolean(value.asBoolean());
         } else if (value.isNull()) {