Bump CMake version and fix warning on arm64

[zhao-shihan]

This pull request updates the build configuration and improves Unicode handling in the codebase. The main changes are an update to the minimum required CMake version and a fix to use the correct type for Unicode interval boundaries.

Build system update:

• Increased the minimum required CMake version to 3.12 and simplified the project configuration in CMakeLists.txt. 3.8 is ancient.

Fix a compilation warning on ARM64:

• Changed the type of interval::first and interval::last from int to wchar_t in both include/indicators/display_width.hpp and single_include/indicators/indicators.hpp. This fixes the following warning on ARM64:

In file included from .../include/indicators/block_progress_bar.hpp:6:
In file included from .../include/indicators/details/stream_helper.hpp:5:
.../include/indicators/display_width.hpp:86:35: warning: comparison of integers of different signs: 'wchar_t' and 'const int' [-Wsign-compare]
   86 |   if (ucs < table[0].first || ucs > table[max].last)
      |                               ~~~ ^ ~~~~~~~~~~~~~~~
.../include/indicators/display_width.hpp:86:11: warning: comparison of integers of different signs: 'wchar_t' and 'const int' [-Wsign-compare]
   86 |   if (ucs < table[0].first || ucs > table[max].last)
      |       ~~~ ^ ~~~~~~~~~~~~~~
.../include/indicators/display_width.hpp:90:13: warning: comparison of integers of different signs: 'wchar_t' and 'const int' [-Wsign-compare]
   90 |     if (ucs > table[mid].last)
      |         ~~~ ^ ~~~~~~~~~~~~~~~
.../include/indicators/display_width.hpp:92:18: warning: comparison of integers of different signs: 'wchar_t' and 'const int' [-Wsign-compare]
   92 |     else if (ucs < table[mid].first)
      |              ~~~ ^ ~~~~~~~~~~~~~~~~
4 warnings generated.

That's because wchar_t can be either signed or unsigned, depending on platform and compilation options.