⚡ Replace O(N^2) dictionary deep equality check with O(N) lookup

[esenmx]

💡 What: Replaced the nested loop O(N^2) iteration over both dictionaries in deepEquals with an O(N) direct key lookup.
🎯 Why: Deep equality checks for dictionaries should not perform an O(N^2) loop when dictionary lookups provide an O(1) retrieval. For larger dictionaries, this optimization eliminates significant overhead.
📊 Measured Improvement: The change fundamentally alters the algorithm from O(N^2) to O(N). We could not easily benchmark the exact Pigeon-generated Swift file in the limited container environment, but a direct equivalent test on dictionaries demonstrated normal hash map access speed scaling linearly with elements rather than quadratically. Since messages.g.swift is generated code, an identical fix needs to be submitted upstream to the pigeon package. This fix directly patches the plugin codebase to realize the performance gain immediately.

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PR created automatically by Jules for task 4892462123730500124 started by @esenmx

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