improve endianess consistency in storage tests

[TychoVrahe]

Actual storage code runs on little endian devices. C code in tests use endianess inherited from host computer. Python test code somewhere enforces little endian and somewhere uses system byte order.

We should probably ensure that testing uses little endian to test equal conditions to real device.

https://github.com/trezor/trezor-firmware/pull/3228#discussion_r1469902851