Fix debug format width calculation

[Satyakam-Mishra]

Fixes #4901.

The width calculation for debug-formatted characters and strings was based on the unescaped output size. This caused incorrect padding for debug characters and could truncate the closing quote for empty debug strings.

This change:

• Calculates the formatted size of debug characters using the escaped representation.
• Correctly accounts for the closing quote of an empty debug string when width/precision permits it.
• Adds regression tests for both cases.

All tests pass locally.

[vitaut]

counting_buffer seems pretty heavyweight here for an output that is at most 12 characters. Could we format once into a small local buffer and use its size for padding, then copy it to the output? Something along the lines of

Char buf[12];
auto* begin = buf;
auto* end = begin;
size_t size = 1;

if (is_debug) {
  end = write_escaped_char(begin, value);
  size = to_unsigned(end - begin);
}

return write_padded<Char>(out, specs, size, [=](auto it) {
  if (is_debug) return copy<Char>(begin, end, it);
  *it++ = value;
  return it;
});

[Satyakam-Mishra]

Thanks! I have updated the implementation to use a small local buffer as suggested, and the tests and clang-format-21 checks passes.

[Satyakam-Mishra]

Updated the implementation to use reserve_iterator instead of generic auto lambda parameter, which was causing the CI build failure with the older compiler. The changes are pushed and the local tests are passing