Add I/O and formatting performance benchmarks

- Add format vs fmt benchmark (format_vs_fmt.cc)
- Add teju vs dragonbox floating point benchmark (teju_vs_dragonbox.cc)
- Add file I/O vs stdio benchmark (file_vs_stdio.cc)

These benchmarks compare fast_io performance against fmt library,
dragonbox/teju floating point implementations, and standard stdio
for various I/O and formatting operations.

Author: puji4810