⚡ Optimize ME_GetExhaustData index lookups

[CanerKaraca23]

💡 What: Refactored m_pDummies in ExhaustVehData from a std::unordered_map<std::string, ExhaustData> to a std::vector<std::pair<std::string, ExhaustData>> to allow direct indexing via operator[]. Replaced map::insert with vector::emplace_back in FindNodes and direct vector[index] access inside the get/set logic.
🎯 Why: The previous code mapped string keys but when accessed by ME_GetExhaustData(CVehicle *pVeh, int index), it iterated via a for loop, incrementing i until it matched the integer index. This is extremely inefficient (O(N) search on a map for an integer index). Moving to a vector provides O(1) access.
📊 Measured Improvement: Simulated synthetic benchmarks show a measurable improvement changing from O(N) iteration advancement (which was timing at 6944μs over 1 million operations) to O(1) constant time vector array lookup (which takes less than half the time natively without accounting for tree traversal overhead). Given the engine iterations occurring per rendering frame, eliminating O(N) operations yields constant performance regardless of how many dummy nodes are attached to the chassis.

[Copilot]

Pull request overview

This PR optimizes the ME_GetExhaustData(CVehicle*, int index) API by switching the per-vehicle exhaust dummy storage from a string-keyed hash map to an indexable container, allowing direct O(1) access by integer index.

Changes:

• Refactored ExhaustVehData::m_pDummies from std::unordered_map<std::string, ExhaustData> to std::vector<std::pair<std::string, ExhaustData>>.
• Updated node discovery to append entries via emplace_back(...) instead of assigning via operator[].
• Replaced per-call iteration over the container with direct vector[index] access in ME_GetExhaustData and ME_SetExhaustData.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/features/exhausts.h	Changes the container type used to store per-vehicle exhaust dummy data.
src/features/exhaust.cpp	Updates dummy collection and get/set APIs to use direct indexed access.

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