Add Actor::FindChild method and expose it to Lua

[Gopmyc]

Description

This PR adds a new Actor::FindChild method to search a child actor by name within an actor hierarchy.

Changes included:

• Added Actor::FindChild(const std::string& p_name, bool p_recursive) const to the C++ Actor API.
• Implemented the search logic in Actor.cpp:
  • first checks direct children,
  • then checks descendants recursively when p_recursive is true,
  • returns the first matching actor or nullptr.
• Exposed FindChild to Lua in LuaActorBindings.
• Updated Lua API stubs (Resources/Engine/Lua/Scene/Actor.lua) with the new method signature.

Related Issue(s)

Fixes #798

Review Guidance

Please review in this order:

1. Sources/OvCore/include/OvCore/ECS/Actor.h (new method declaration)
2. Sources/OvCore/src/OvCore/ECS/Actor.cpp (method implementation)
3. Sources/OvCore/src/OvCore/Scripting/Lua/Bindings/LuaActorBindings.cpp (Lua binding)
4. Resources/Engine/Lua/Scene/Actor.lua (Lua API stub update)

Screenshots/GIFs

N/A

AI Usage Disclosure

N/A

Checklist

• My code follows the project's code style guidelines
• When applicable, I have commented my code, particularly in hard-to-understand areas
• When applicable, I have updated the documentation accordingly
• My changes don't generate new warnings or errors
• I have reviewed and take responsibility for all code in this PR (including any AI-assisted contributions)