fix(context): correct `ResultGas::final_refunded()` when floor gas is active
The previous implementation (`spent - used()`) returned incorrect values
when EIP-7623 floor gas kicked in. Now returns `0` when floor gas absorbs
the refund, and the raw refund otherwise. Adds clarifying docs and tests.
fix(context): correct `ResultGas::final_refunded()` when floor gas is active
The previous implementation (`spent - used()`) returned incorrect values
when EIP-7623 floor gas kicked in. Now returns `0` when floor gas absorbs
the refund, and the raw refund otherwise. Adds clarifying docs and tests.