Change: Replace loosen-follower-log-revert feature flag with Config::allow_log_reversion

[drmingdrmer]

Changelog

Change: Replace loosen-follower-log-revert feature flag with Config::allow_log_reversion

The loosen-follower-log-revert feature flag is removed in favor of a
runtime-configurable option, Config::allow_log_reversion. This change
allows log reversion to be controlled dynamically via application
configuration rather than at compile time.

When Config::allow_log_reversion is enabled, log reversion on a
Follower is always permitted. Upon detecting a reversion, the Leader
will reset replication from the beginning instead of panicking.

Breaking Change:

Since this commit, compiling with --features loosen-follower-log-revert will now result in the following error:

error: The feature flag `loosen-follower-log-revert` is removed since version `0.10.0`.
       Use `Config::allow_log_reversion` instead.

Upgrade tip:

For applications relying on loosen-follower-log-revert:

1. Remove this feature flag from Cargo.toml.
2. Enable log reversion in your configuration as follows:

let config = Config {
    allow_log_reversion: Some(true),
    ..Default::default()
};

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This change is 

[schreter]

Reviewed 21 of 21 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @drmingdrmer)

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openraft/src/progress/entry/update.rs line 35 at r1 (raw file):

    ///
    /// [`Config::allow_log_reversion`]: `crate::config::Config::allow_log_reversion`
    pub(crate) fn update_conflicting(&mut self, conflict: u64) {

I assume, this was just moved from above, so I didn't review.

[drmingdrmer]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @drmingdrmer)

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openraft/src/progress/entry/update.rs line 35 at r1 (raw file):

Previously, schreter wrote…

I assume, this was just moved from above, so I didn't review.

Yes. In order to reference EngineConfig, it is moved to a dedicate Updater without changes.