The `aligner.rs` file was only growing in size, rendering navigation
complicated. This commit splits it in the following manner:
- `aligner_query.rs` inherits the `AlignmentQuery` and the logic that
  generates a reply to it.
- `aligner_reply.rs` inherits the `AlignmentReply` and the logic to
  process it.
- `core.rs` inherits the `spawn_query_replica_aligner` that spawns a
  task to query the "Aligner" of a Replica.

* plugins/zenoh-plugin-storage-manager/src/replication/aligner.rs:
  deleted and split the content of the file.

* plugins/zenoh-plugin-storage-manager/src/replication/core.rs:
  - Declared the new modules `aligner_query` and `aligner_reply`.
  - Updated the imports as the method `spawn_query_replica_aligner`
    was moved there.

* plugins/zenoh-plugin-storage-manager/src/replication/core/aligner_query.rs:
  new file that holds the logic to generate a reply to an AlignmentQuery.

* plugins/zenoh-plugin-storage-manager/src/replication/core/aligner_reply.rs:
  new file that holds the logic to process an AlignmentReply.

* plugins/zenoh-plugin-storage-manager/src/replication/mod.rs: removed
  the, no longer used, module `aligner`.

Signed-off-by: Julien Loudet <julien.loudet@zettascale.tech>

This commit adds the method `remove_older` to the `LogLatest`
structure. The motivation for this addition is to later optimise the
alignment by only searching through the Replication Log once when
replacing / adding Events.

To make the rest of the code more coherent, the method
`if_newer_remove_older` were renamed to `remove_older` for the
`Interval` and `SubInterval` structures.

* plugins/zenoh-plugin-storage-manager/src/replication/classification.rs:
  - Renamed `if_newer_remove_older` to `remove_older` for the Interval
    structure.
  - Renamed `if_newer_remove_older` to `remove_older` for the
    SubInterval structure.
  - Added a line in the documentation of both `remove_older` methods to
    indicate that their respective Fingerprint would be updated.

* plugins/zenoh-plugin-storage-manager/src/replication/log.rs:
  - Updated the method `insert_event` to leverage the newly created
    `remove_older` method.
  - Added the `remove_older` method that removes from the Replication
    Log an older Event on the same key expression.

* plugins/zenoh-plugin-storage-manager/src/replication/tests/classification.test.rs:
  updated the calls to `remove_older` due to the renaming.

Signed-off-by: Julien Loudet <julien.loudet@zettascale.tech>

This renaming makes the content of this variant clear: only the metadata
is processed.

* plugins/zenoh-plugin-storage-manager/src/replication/core/aligner_query.rs:
  renamed `AlignmentReply::Events` to `AlignmentReply::EventsMetadata`.
* plugins/zenoh-plugin-storage-manager/src/replication/core/aligner_reply.rs:
  renamed `AlignmentReply::Events` to `AlignmentReply::EventsMetadata`,
  including in logging.

Signed-off-by: Julien Loudet <julien.loudet@zettascale.tech>

This commit moves, for clarity purposes, the logic to process an
`EventMetadata` after receiving an `AlignmentReply::EventsMetadata` in a
separate method: `process_event_metadata`.

This notably removes indentation levels and makes the code more
readable.

* plugins/zenoh-plugin-storage-manager/src/replication/core/aligner_reply.rs:
  move the logic to process an `EventMetadat` in a separate method
  `process_event_metadata`.

Signed-off-by: Julien Loudet <julien.loudet@zettascale.tech>

This commit moves, for clarity purposes, the logic to process an
`Retrieval` in a separate method: `process_event_retrieval`.

This notably removes indentation levels and makes the code more
readable.

* plugins/zenoh-plugin-storage-manager/src/replication/core/aligner_reply.rs:
  move the logic to process a `Retrieval` in a separate method
  `process_event_retrieval`.

Signed-off-by: Julien Loudet <julien.loudet@zettascale.tech>

Before this commit, the Replication Log was searched twice when aligning
an Event: once while calling `lookup` and a second time when calling
`insert_event`.

To reduce the number of searches to a single one, the method
`insert_event_unchecked` was introduced. This function assumes that the
Replication Log contains no Event with the same key expression as the
Event it will insert.

Leveraging this, the calls to `LogLatest::lookup` followed by
`LogLatest::insert_event` were replaced with calls to
`LogLatest::remove_older` followed by
`LogLatest::insert_event_unchecked`.

Indeed, if the call to `LogLatest::remove_older` yields either
`NotFound` or `RemovedOlder` then the Replication Log does not contain
any event with the key expression, and
`LogLatest::insert_event_unchecked` can be confidently called.

Another consequence of the introduction of the new method
`insert_event_unchecked` is that the variant
`EventInsertion::NotInsertedAsOutOfBound` was no longer used and was
thus removed.

* plugins/zenoh-plugin-storage-manager/src/replication/core/aligner_reply.rs:
  Replaced the calls to `lookup` followed by `insert_event` to calls
  to `remove_older` followed by `insert_event_unchecked` in the
  methods `process_event_metadata` and `process_event_retrieval`.

* plugins/zenoh-plugin-storage-manager/src/replication/log.rs:
  - Removed the no longer used `EventInsertion::NotInsertedAsOutOfBound`
    variant.
  - Added a comment to clearly indicate that the method `insert_event`
    will remove older Event.
  - Introduced the new method `insert_event_unchecked` that inserts an
    Event in the Replication Log without checking if it is the only
    Event (i.e. it assumes it is the case).

Signed-off-by: Julien Loudet <julien.loudet@zettascale.tech>

This commit introduces an assertion test every time an Event in inserted
in the Replication Log ONLY IN DEBUG.

The purpose is to make sure that the invariant of the Replication Log is
upheld: it should only contain one Event per key expression.

* plugins/zenoh-plugin-storage-manager/src/replication/classification.rs:
  added the method `assert_only_one_event_per_key_expr` to the
  `Interval` and `SubInterval` structures.

* plugins/zenoh-plugin-storage-manager/src/replication/log.rs: added the
  method `assert_only_one_event_per_key_expr` to the `LogLatest`
  structure.

Signed-off-by: Julien Loudet <julien.loudet@zettascale.tech>