feat: implement sha256t

[rkdud007]

#5

• so the std implementation of Sha256 doesn't have exposed method around middlestate. as sha256t works with middlestate alot, decided to have Hashengine that embeds std sha256.

• I opened a draft PR because I want to check if the approach makes sense along the way.

• especially i found type casting with [32]u8 <> [8]u32 bit tricky not sure if this most standard way to cast