Expose Actor.GetGUID() as hex string in Lua

[Gopmyc]

Description

This PR exposes Actor::GetGUID() to Lua through the Actor bindings and returns it as a fixed-width hexadecimal string ({:016X}).

Related Issue(s)

Fixes #779

Review Guidance

• Check LuaActorBindings.cpp for the new GetGUID Lua method.
• Confirm the return format is uppercase 16-char hexadecimal string.
• Check Resources/Engine/Lua/Scene/Actor.lua for the matching 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)