Remove MPI dependence in Logger

[cniethammer]

Description

This PR removes all dependencies to MPI inside the Logger class. The functionality was replaced by a general message prefix and setting the log levels for the different MPI processes.
Note: By default, MPI processes with rank zero will use log level Info and all other MPI processes log level Error. This should help in identifying errors more quickly from logs. As a side effect, the --verbose option will now enable log level All for all MPI processes, which should be helpful for debugging.

Related Pull Requests

• This is also in preparation of Use MPI_Init_thread if OpenMP is enabled #306

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

• running examples
• running unit tests

[HomesGH]

To fix issue #374, we should perform a case-insensitive comparison here. This could be done by changing these lines:

ls1-mardyn/src/utils/Logger.h

Lines 191 to 197 in 2981975

	logLevel set_log_level(std::string l) {
	for (const auto& [lvl, name] : logLevelNames) {
	if (name == l) {
	_log_level = lvl;
	return _log_level;
	}
	}

to:

	logLevel set_log_level(std::string l) {
	// Compare case-insensitive
	std::string l_lower = l;
	std::transform(l_lower.begin(), l_lower.end(), l_lower.begin(), ::tolower);
	for (const auto& [lvl, name] : logLevelNames) {
		std::string name_lower = name;
		std::transform(name_lower.begin(), name_lower.end(), name_lower.begin(), ::tolower);
		if (name_lower == l_lower) { 
			_log_level = lvl; 
			return _log_level; 
		} 
	}

[amartyads]

If we do toUpper instead, we can avoid multiple conversions:

	logLevel set_log_level(std::string l) {
	// Compare case-insensitive
	std::string l_upper = l;
	std::transform(l_upper.begin(), l_upper.end(), l_upper.begin(), [](unsigned char c){ return std::toupper(c);});
	for (const auto& [lvl, name] : logLevelNames) {
		if (name == l_upper) { 
			_log_level = lvl; 
			return _log_level; 
		} 
	}

The lambda function is to avoid undefined behaviour (https://en.cppreference.com/w/cpp/string/byte/toupper)