Cost estimations must reset between 2.0 and 2.05 epoch

[kantai]

Cost estimations for contract-call invocations in 2.05 and 2.00 must be reset -- the costs of contract-calls will all change because of the new cost functions, methods of calculating input, etc.

This should be relatively easy to implement -- the cost estimator should just add an epoch identifier to the key used as a cost identifier:

    fn get_estimate_key(tx: &TransactionPayload, field: &CostField, evaluated_epoch: &StacksEpochId) -> String {
        let tx_descriptor = match tx {
            TransactionPayload::TokenTransfer(..) => "stx-transfer".to_string(),
            TransactionPayload::ContractCall(cc) => {
                let epoch_marker = match evaluated_epoch {
                     StacksEpochId::Epoch10 => "",
                     StacksEpochId::Epoch20 => "",
                     StacksEpochId::Epoch2_05 => ":2.05",
                };
                format!("cc{}:{}.{}", epoch_marker, cc.contract_name, cc.function_name)
            }
            TransactionPayload::SmartContract(_sc) => "contract-publish".to_string(),
            TransactionPayload::PoisonMicroblock(_, _) => "poison-ublock".to_string(),
            TransactionPayload::Coinbase(_) => "coinbase".to_string(),
        };

        format!("{}:{}", &tx_descriptor, field)
    }

This will separate the estimates of functions evaluated in 2.05 from those evaluated in 2.00.

[kantai]

For testing this, I believe it's sufficient to unit test. Basically, add a new test or set of tests in the src/cost_estimates/tests/cost_estimators.rs module that:

1. supply measurements with the evaluated_epoch = 2.0
2. fetch estimates using 2.05, asserting that no estimate is available
3. fetch estimates using 2.00, asserting that an estimate is available
4. supply different measurements with the evaluated_epoch = 2.05
5. fetch estimates using 2.05, asserting that the estimate is available, and is different than the 2.00 estimate
6. fetch estimate using 2.00, asserting that its still the same as it was in step 3