⚡ Bolt: Avoid redundant getenv calls and string formats

[ManupaKDU]

💡 What: Store the results of getenv() and formatted strings into local variables instead of calling them multiple times for the same values in scripts/json_add_image_info.py.
🎯 Why: Repeatedly formatting strings and accessing os.getenv adds unnecessary function call and string allocation overheads. Caching the result in a local variable is faster and more readable.
📊 Impact: Eliminates dozens of redundant function calls per execution, slightly speeding up JSON metadata generation.
🔬 Measurement: Verify changes with unit tests and ensure no syntax regressions occur using py_compile.

Signed-off-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

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PR created automatically by Jules for task 198602680546303440 started by @manupawickramasinghe

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