token 2022: add alloc_and_serialize for fixed-len extensions (#5672)

* token 2022: add alloc_and_serialize for fixed-len extensions

* add tandem try_get_new_account_len functions

* refactor alloc_and_serialize

* added tests for alloc_and_serialize (fixed)

* address feedback

Author: Joe C

token/client/src/token.rs

@@ -3458,7 +3458,8 @@ where
         let account = self.get_account(self.pubkey).await?;
         let account_lamports = account.lamports;
         let mint_state = self.unpack_mint_info(account)?;
-        let new_account_len = mint_state.try_get_new_account_len(token_metadata)?;
+        let new_account_len = mint_state
+            .try_get_new_account_len_for_variable_len_extension::<TokenMetadata>(token_metadata)?;
         let new_rent_exempt_minimum = self
             .client
             .get_minimum_balance_for_rent_exemption(new_account_len)
@@ -3540,7 +3541,8 @@ where
         let mint_state = self.unpack_mint_info(account)?;
         let mut token_metadata = mint_state.get_variable_len_extension::<TokenMetadata>()?;
         token_metadata.update(field, value);
-        let new_account_len = mint_state.try_get_new_account_len(&token_metadata)?;
+        let new_account_len = mint_state
+            .try_get_new_account_len_for_variable_len_extension::<TokenMetadata>(&token_metadata)?;
         let new_rent_exempt_minimum = self
             .client
             .get_minimum_balance_for_rent_exemption(new_account_len)