Progress bar fixes

[ziuziakowska]

• In the first second of an operation, the time shows as ,, and then goes to 1s, after a second has elapsed. Update this to display seconds always (e.g 0s, -> 1s,, 59s, -> 1m0s,) so that even if an operation took no time at all it still shows the duration.
• If the printed length of the throughput section shrunk in size (e.g rate measured in XXX KiB/s rises to X MiB/s), garbage characters would be visible at the end of the line (usually an additional /s). Track the last printed width so that if it gets smaller, the difference is overwritten with spaces, and then backspace to the current printed length.

[engdoreis]

Using width padding is more idiomatic, I didn't test, but I think this would work?

Suggested change

	std::cout << "] " << percent_str << "\033[33m" << " " << tp_str << "\033[0m";
	if (tp) {
	if (this->last_length > print_length) {
	/* There are some trailing characters left over from the last
	* time throughput was printed. Overwrite them with spaces,
	* and then backspace to the current length. */
	int diff = this->last_length - print_length;
	for (int i = 0; i < diff; i++) {
	std::cout << " ";
	}
	for (int i = 0; i < diff; i++) {
	std::cout << "\b";
	}
	}
	int size = std::max(this->last_length, print_length);
	auto bar = std::format( "] {} \033[33m {} \033[0m", percent_str, tp_str);
	std::print("{:<{}}\b", bar, size);

[ziuziakowska]

This would work in overwriting the excess text, but this would only backspace once at the end, and not back to the current length of the line, so there would be some trailing spaces. I think although padding lets you choose an arbitrary padding character, it cannot be used to just print a character n times as padding is part of a full format specifier.

[ziuziakowska]

I've tried to make it more idiomatic/less noisy, what do you think?