epic: ensure no operation overflows

[enitrat]

Ensure that no operation overflows.

example, in returndatacopy:

    fn exec_returndatacopy(ref self: VM) -> Result<(), EVMError> {
        let dest_offset = self.stack.pop_usize()?;
        let offset = self.stack.pop_usize()?;
        let size = self.stack.pop_usize()?;
        let return_data: Span<u8> = self.return_data();

        let (last_returndata_index, overflow) = offset.overflowing_add(size);
        if overflow {
            return Result::Err(EVMError::ReturnDataOutOfBounds);
        }
        ensure(!(last_returndata_index > return_data.len()), EVMError::ReturnDataOutOfBounds)?;

instead of doing size + offset to get the last returndata index, we check for overflows. Otherwise, we would get a CairoVM error that would fail the entire transaction

we can use something like

offset.overflowing_add(size).ok_or(EVMError::ReturnDataOutOfBounds)?;

to manage this efficiently

[onlydustapp]

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