feat(skymp5-server): add onReadBook event

[Pospelove]

[!IMPORTANT] Adds ReadBookEvent to handle book reading in MpActor, updating learned spells and logging events.

• Behavior:
  • Introduces ReadBookEvent to handle book reading in MpActor::ReadBook().
  • Logs error if book form not found and logs unimplemented skill book handling.
  • Updates actor's learned spells if the book teaches a spell.
• Event Handling:
  • ReadBookEvent class added with methods GetName(), GetArgumentsJsonArray(), SpellLearned(), and OnFireSuccess().
  • OnFireSuccess() checks if the spell is already learned and updates the change form.
• Misc:
  • Removes previous book reading logic from MpActor::ReadBook() and replaces it with ReadBookEvent firing.

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