Make releasedata.Product usable in 'with' expression (#294)

This way the writing of the JSON file is handled automatically if the update does not fail.
It pave the way to further global improvements, such as a better error handling.

src/npm.py

@@ -6,14 +6,12 @@ METHOD = "npm"
 
 p_filter = sys.argv[1] if len(sys.argv) > 1 else None
 for product in endoflife.list_products(METHOD, p_filter):
-    product_data = releasedata.Product(product.name)
-    for config in product.get_auto_configs(METHOD):
-        data = http.fetch_url(f"https://registry.npmjs.org/{config.url}").json()
-        for version_str in data["versions"]:
-            version_match = config.first_match(version_str)
-            if version_match:
-                version = config.render(version_match)
-                date = dates.parse_datetime(data["time"][version_str])
-                product_data.declare_version(version, date)
-
-    product_data.write()
+    with releasedata.ProductData(product.name) as product_data:
+        for config in product.get_auto_configs(METHOD):
+            data = http.fetch_url(f"https://registry.npmjs.org/{config.url}").json()
+            for version_str in data["versions"]:
+                version_match = config.first_match(version_str)
+                if version_match:
+                    version = config.render(version_match)
+                    date = dates.parse_datetime(data["time"][version_str])
+                    product_data.declare_version(version, date)