⚡ Bolt: WasmJs ThemeCache Optimization

[himattm]

💡 What: In-memory cache for LocalStorageThemeCache.kt manifest in wasmJs targets. Added a nullable manifestCache that holds the decoded JSON contents to skip the decoding over and over on operations involving the manifest. Added a learning to bolt.md detailing the overhead of string manipulation and JSON decoding on WasmJs targets.
🎯 Why: Each time we interact with the cache in wasmJs we read localStorage using JS Interop and decoded the resulting raw strings to Set<String> using kotlinx.serialization. This avoids doing it if not needed or caching it in-memory for recurrent use.
📊 Impact: Reduces overhead time when parsing data or clearing it out for recurrent operations. Avoids duplicate reads and calls.
🔬 Measurement: Verify changes looking at LocalStorageThemeCache.kt. Use wasmJsBrowserTest task to check for changes and test functionality.

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PR created automatically by Jules for task 10350852678019541139 started by @himattm

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