* add gas argument

* Add gas parameter to ext_gas_price

* Fix up gas_price offchain api

* Fix up env_access api

* Emulate gas price calculation

* Make clippy happy

* Use Saturating impl for emulating gas price calculation offchain

* Fmt

* Add offchain gas_price test

* Make clippy happy

* extract arithmetic types

* Add basic saturating tests

* Fmt

* Add comment about EnvTypes bounds