Investigate struct ordening u256 in Cairo and Native/Blockifier

[xrvdg]

Accessing the high part of a U256 from within Rust gives the same result as accessing the low part of u256 from within Cairo. This seems to point to the order of the struct getting mixed up. We currently workaround this in both keccak and secp in the native starknet sycall handler.

[xrvdg]

Opened a ticket for it on the cairo native repo: lambdaclass/cairo_native#715

[xrvdg]

This has been fixed in lambdaclass/cairo_native#720.

We need to update our keccak and secp when bumping our dependency on cairo native to a commit after lambdaclass/cairo_native@9527cc9.