Fantom chain (#806)

* feat(core): add fantom and fantom-testnet chains

* feat(etherscan): add fantom chains support

* chore: lint

ethers-core/src/types/chain.rs

@@ -21,6 +21,8 @@ pub enum Chain {
     Kovan = 42,
     XDai = 100,
     Polygon = 137,
+    Fantom = 250,
+    FantomTestnet = 4002,
     PolygonMumbai = 80001,
     Avalanche = 43114,
     AvalancheFuji = 43113,
@@ -102,6 +104,8 @@ impl FromStr for Chain {
             "moonriver" => Chain::Moonriver,
             "optimism" => Chain::Optimism,
             "optimism-kovan" => Chain::OptimismKovan,
+            "fantom" => Chain::Fantom,
+            "fantom-testnet" => Chain::FantomTestnet,
             _ => return Err(ParseChainError(chain.to_owned())),
         })
     }

ethers-etherscan/src/lib.rs

@@ -66,6 +66,13 @@ impl Client {
                 Url::parse("https://api-kovan-optimistic.etherscan.io/api"),
                 Url::parse("https://kovan-optimistic.etherscan.io"),
             ),
+            Chain::Fantom => {
+                (Url::parse("https://api.ftmscan.com"), Url::parse("https://ftmscan.com"))
+            }
+            Chain::FantomTestnet => (
+                Url::parse("https://api-testnet.ftmscan.com"),
+                Url::parse("https://testnet.ftmscan.com"),
+            ),
             chain => return Err(EtherscanError::ChainNotSupported(chain)),
         };
 
@@ -89,7 +96,9 @@ impl Client {
             Chain::Rinkeby |
             Chain::Goerli |
             Chain::Optimism |
-            Chain::OptimismKovan => std::env::var("ETHERSCAN_API_KEY")?,
+            Chain::OptimismKovan |
+            Chain::Fantom |
+            Chain::FantomTestnet => std::env::var("ETHERSCAN_API_KEY")?,
 
             Chain::XDai | Chain::Sepolia => String::default(),
             Chain::Moonbeam | Chain::MoonbeamDev | Chain::Moonriver => {