Feat: Implement faster cost tracker for default cost functions

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to the versioning scheme outlined in the [README.md](RE
 
 ### Changed
 
+- Implement faster cost tracker for default cost functions in Clarity
 - Miner will stop waiting for signatures on a block if the Stacks tip advances (causing the block it had proposed to be invalid).
 - Logging improvements:
   - P2P logs now includes a reason for dropping a peer or neighbor

clarity/src/vm/contexts.rs

@@ -715,6 +715,10 @@ impl<'a, 'hooks> OwnedEnvironment<'a, 'hooks> {
         })
     }
 
+    pub fn is_mainnet(&self) -> bool {
+        self.context.mainnet
+    }
+
     #[cfg(any(test, feature = "testing"))]
     pub fn stx_faucet(&mut self, recipient: &PrincipalData, amount: u128) {
         self.execute_in_env::<_, _, crate::vm::errors::Error>(