speeded up game exports for large projects by optimizing file lookups

[brolookslikeanfish67-hub]

Description

This PR optimizes the file compilation loop within the GDJS Exporter pipeline (GDJS/IDE/Exporter.cpp).

The Problem:

InsertUnique was executing a sequential std::find check on std::vector lists for every source, dependency, library, and asset requirement during an export pipeline. This created a standard O(N²) computational bottleneck for complex visual game projects containing heavily scaled modular extension libraries.

The Fix:

• Transitioned uniquely tracked resource lists to stack-allocated tracking blocks using std::unordered_set hash lookups. This drops insertion checking from O(N) down to O(1).
• Encapsulated helper functionality cleanly inside an anonymous namespace to avoid polluting the global file space.
• Swapped gd::String value parameters out for const gd::String& references inside local scope definitions to drop memory allocation requirements entirely.
• Modernized explicit class destructor mappings to use contemporary = default; architecture.

Why this is safe:

The tracking sets are completely stack-contained inside exportProject. This prevents permanent class-level state inflation while maintaining full algorithmic optimizations during hot paths.