TStringBuffer over TStringBuilder

Date: 2026-03-11 Area: strings Pull Request: #65

TStringBuffer over TStringBuilder. Both TUnicodeStringBuilder and TAnsiStringBuilder trigger a 750× slowdown from FPC's heap manager without preallocation. TStringBuffer (advanced record with doubling growth) is ~2× faster even with preallocation. #65. spikes/fpc-string-performance.md.