maybe add API: ed.get_char_count()

[Alexey-T]

Editor.get_char_count(max_chars, max_time)

return count of chars in document. EOL is counted as 1.

• if result becomes bigger than max_chars (it can be 0x7fffFFFF to avoid limit), return -1.
• if working time is bigger than max_time (in mseconds, it can be 0x7fffFFFF to avoid limit) return -2.

it will be faster version of python function which I shown to @pintassilgo. python version of code calls ed.get_line_len() in loop which is SLOW.