Provides *debug log* which can be written to, but does not affect the host state.

The result of writing to the debug log is *implementation specific* - it may, for
example, be written to a log file, or to `stdout` etc.

The `debug_msg` macro supports inline formatting:

```no_run
extern crate alloc;
use mavryk_smart_rollup_debug::debug_msg;
use mavryk_smart_rollup_host::runtime::Runtime;

fn log_runtime(host: &impl Runtime) {
  debug_msg!(host, "Simple constant string");

  debug_msg!(host, "A format {} with argument {}", "test", 5);
}
```

In the simplest case, however, one can also write:

```no_run
use mavryk_smart_rollup_host::runtime::Runtime;

fn log_simple(host: &impl Runtime) {
    host.write_debug("A simple constant string");
}
```