[agustux]

Fixes #16

bin2header.cmake iterated once per byte and expanded the full hex
string each time (O(n^2)). For the bundled font, the build appeared to
hang; the old script did not finish when I cancelled it.

This replaces the loop with two string(REGEX REPLACE) passes:

1. Each hex pair from file(READ ... HEX) is rewritten in place as
   0xNN,. Pairs are replaced independently, so values and order are
   unchanged.
2. A second pass inserts a newline and indent after every 12 entries.
   It adds whitespace only.

The script's interface (INPUT, OUTPUT, ARRAY_NAME) is unchanged,
so CMakeLists.txt and main.c are untouched. Only commands available
in CMake 3.19+ are used, and comments explain why, per AGENTS.md.

Output differs from the old script only in whitespace and a trailing
comma after the last element, which is valid C.

Tested:

• cmake -B build -G Ninja && cmake --build build succeeds (Debug)
• cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release && cmake --build build succeeds, and ./build/ghostling runs
• On a 2000-byte input, old and new output are identical after
  stripping whitespace and the trailing comma
• New script time on the font: 0.483s (old script did not finish)

Note: running the Debug build (./build/ghostling) panics with
"incorrect alignment" in libghostty's ghostty_terminal_set. This is
outside this change (main.c and libghostty are untouched).