Add a writer that transform items before delegating to another writer

[yann-eugone]

This one might be a game changer, combined with recent additions.we will be able to do many things in write process.

Example :

new ItemJob(
    500, 
    new JsonLinesReader(/* dependencies */),
    /* your processor that convert json line to an entity*/,
    new ChainWriter(
        [
            new ObjectWriter(/* dependencies */),
            new ConditionalWriter(
                fn ($entity) => /* your condition to detect entity was created */,
                new TransformingWriter(
                    new CallbackProcessor(fn () => new NewEntityCreated()),
                    new DispatchEachItemAsMessageWriter(/* dependencies */)
                )
            ),
        ]
    ), 
    /*  dependencies  */
);

• read from a json file
• convert each line to an entity
• persist/flush each converted entities
• if entity is new, dispatch a message in the bus

[codecov]

Codecov Report

Merging #65 (08af435) into 0.x (69b3cf6) will not change coverage.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##                 0.x       #65   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       724       734   +10     
===========================================
  Files            124       125    +1     
  Lines           1846      1871   +25     
===========================================
+ Hits            1846      1871   +25     

Impacted Files	Coverage Δ
...c/batch/src/Job/Item/Writer/TransformingWriter.php	100.00% <100.00%> (ø)

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