blake2engine: Use .data() to get pointer to data and not .begin()

[autoantwort]

.begin() could return an iterator object depending on the build context

[yspolyakov]

@autoantwort We typically create issues and discuss them before creating PRs. I see many small PRs from you (which is overwhelming), and their motivation is not clear. My suggestion is to create one PR with all small fixes/cleanups, and we can later discuss these together. For the time being, I will close the PRs that have been open.

[autoantwort]

So you prefer one big PR with many unrelated changes instead of one PR per concern?
Should I create one Issue for every PR / Concern or one Big one?

[yspolyakov]

I suggest discussing the problem first. We want to understand the motivation before reviewing the PRs. Many PRs appeared very small. You can create an issue for each separate problem. A PR can afterwards be created for multiple issues.

[autoantwort]

I have created #770