⚡ Bolt: Optimize opkg index parsing in make-sbom

[ManupaKDU]

💡 What: Replaced text.splitlines() and generic dictionary building with direct str.find() lookups to extract specific fields when parsing opkg index files. Added early check to skip blocks for packages not in the installed list.
🎯 Why: To significantly improve the speed and reduce memory allocations when generating SBOMs from large opkg index files containing tens of thousands of packages.
📊 Impact: Reduces processing time of 50,000 packages from ~0.75s to ~0.28s.
🔬 Measurement: Measured using a local script generating 50,000 mock packages and parsing them with make-sbom.py.

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 12592403813864266013 started by @manupawickramasinghe

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