[Tcode-Motion]

💡 What: Optimized fstring_concat in techscript_builtins by pre-allocating String capacity based on argument types and appending Value::Str using push_str instead of going through write! formatting macro.

🎯 Why: Previously, fstring_concat started with an unallocated String::new() and repeatedly formatted arguments using write!(res, "{}", arg), causing multiple buffer allocations/reallocations and formatting overhead for strings.

📊 Impact: Reduces string allocations and formatting overhead during f-string evaluations in TechScript programs.

🔬 Measurement: Measured with bench_fstring_concat in builtins_tests.rs across 100,000 f-string concatenation operations (reduced execution time from ~199.19ms to ~162.84ms, an ~18% improvement in debug build testing).

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PR created automatically by Jules for task 10688590165131012732 started by @Tcode-Motion

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