driver-adapters: Rename ColumnType::Char to Character

[SevInf]

To avoid confusion with SQL's CHAR type that is a fixed-length string,
not single character.

[codspeed-hq]

CodSpeed Performance Report

Merging #4402 will degrade performances by 5.47%

_{Comparing refactor/char (ce95861) with main (49b44c5)}

Summary

❌ 1 regressions
✅ 10 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	refactor/char	Change
❌	large_read	7.2 ms	7.6 ms	-5.47%