T15906 onconstruct cached model

[niden]

Hello!

• Type: bug fix
• Link to issue: [BUG]: getSnapshotData returns null #15837 [BUG]: onConstruct Model doesn't work as expected with cached instance of the model #15906

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• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

Fixed Phalcon\Mvc\Model::__unserialize() and Phalcon\Mvc\Model::unserialize() to call onConstruct() after deserialization, so typed properties initialized in onConstruct are correctly set when a model is restored from cache

Fixed Phalcon\Mvc\Model::__unserialize() and Phalcon\Mvc\Model::unserialize() to restore snapshot as the current attributes (instead of null) when a model is deserialized with no pending changes, preventing getChangedFields() from throwing after cache retrieval