Improve performance of time and column conversions

[Cybermaxke]

• Improved time based conversion performance by avoiding calendar creation
  • Epoch millis calculation avoids toInstant() where possible to avoid extra allocations
• Improved column name generation by caching frequently used ones (1024 should be enough?)
• Added value setter for Instant to pass UTC based timestamps, no conversions based on system time zone
• Adjusted the benchmark to use LocalDateTime instead of Date to reduce extra conversions

Before:
WriterBenchmark.fastExcel    ss   15  0,219 ± 0,004   s/op

After:
WriterBenchmark.fastExcel    ss   15  0,194 ± 0,010   s/op