Remove From [u8; n] impl for uint types

[pgherveou]

Changes:

• removes the From [u8; n] conversions implementations. Since uint types can be both encoded with little-endian or big-endian format, the From implementation can easily be misused.
• to_big_endian and to_little_endian are renamed write_as_*
• to_little_endian and to_big_endian are now functions that returns the bytes array

[pgherveou]

Thanks. The From implementation already bit me when converting from little endian.

I am not sure of we should also bump the version in this PR or if this is done at release time.

Looks like bumping is done in releases, I can update the changelogs once this is approved by owners

[athei]

FWIW the alloy_primitives U256 doesn't support this conversion neither (although I don't know the exact reason).

Implementing From where the conversion isn't obvious is against the API guidelines. See the last point here. They even mention bytes to number conversion as an explicit example where to not implement it.

[ordian]

Looks like bumping is done in releases, I can update the changelogs once this is approved by owners

Updating the changelogs should ideally happen in the PR itself. If you want to release a new version straight away, you can also bump the versions here. Note that this breaking change will propagate to other crates like primitive-types. It's also a good practice to write how to migrate to a new version in the changelog (this method removed, use that instead).

Releasing a new version then should be easy: https://github.com/paritytech/parity-common/blob/master/CONTRIBUTING.md#releasing-a-new-version

[ordian]

FWIW the alloy_primitives U256 doesn't support this conversion neither (although I don't know the exact reason).

Implementing From where the conversion isn't obvious is against the API guidelines. See the last point here. They even mention bytes to number conversion as an explicit example where to not implement it.

Agreed. This code in uint is very old and predates these guidelines probably.