Prints formatted text to the Valgrind output channel.
This macro wraps the C client request `VALGRIND_PRINTF`. It behaves similarly to
[`std::println`](std.println) in terms of syntax, accepting a format string and
a list of arguments.
# Mechanics
The formatted string is sent to the Valgrind log (typically stderr). Output is
buffered in the client process until the Valgrind tool initializes, at which
point the buffer is flushed.
**Note:** If the process runs **without** Valgrind, this macro does nothing (it
is a no-op). It does not print to stdout or stderr.
## Note
Requires Valgrind **3.0** or higher.