Refactor: remove NodeIdEssential and NodeEssential traits

[drmingdrmer]

Changelog

Refactor: remove NodeIdEssential and NodeEssential traits

These two traits are used to simplify NodeId and Node constraints.
But with Optional* traits, these two are no longer needed.

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This change is 

[schreter]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @drmingdrmer)

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openraft/src/base/mod.rs line 62 at r1 (raw file):

/// A trait that combines all optional features.
#[doc(hidden)]

Do you really want to hide the docs? OTOH, other OptionalT docs are hidden as well.

[drmingdrmer]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @drmingdrmer)

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openraft/src/base/mod.rs line 62 at r1 (raw file):

Previously, schreter wrote…

Do you really want to hide the docs? OTOH, other OptionalT docs are hidden as well.

You're right. We should keep the OptionalT docs visible for consistency and better discoverability. I'll update the documentation settings.