⚡ Bolt: Optimize HTML string generation in calltree_analysis.py

[WarGloom]

💡 What: Replaced repetitive string concatenation (+=) with a list accumulation (.append()) and .join() in create_calltree and html_create_dedicated_calltree_file functions within src/fuzz_introspector/analyses/calltree_analysis.py. Added # Performance Optimization: inline comments.
🎯 Why: In Python, repetitive string concatenation for large strings creates a significant O(N^2) memory reallocation bottleneck. Using list accumulation and .join() is an O(N) operation and improves performance significantly.
📊 Impact: Speeds up call tree HTML generation time (e.g. test_calltree runtime dropped from ~2.19s to ~0.62s).
🔬 Measurement: Can be verified by running PYTHONPATH=src python3 -m pytest src/test/ -k "test_calltree" --ignore=src/test/fuzz/ before and after the change.

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PR created automatically by Jules for task 18423711959033759850 started by @WarGloom

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