Save provenance tracking info from grid file

[johnomotani]

Save (if present) the grid_id, hypnotoad_version, hypnotoad_git_hash, hypnotoad_git_diff and hypnotoad_geqdsk_filename. I've checked that this works on the v4.4 backport using a gridfile generated with a recent version of hypnotoad.

Also update the docs to note useful attributes/variables for reproducibility and provenance tracking.

[github-actions]

clang-tidy made some suggestions

[johnomotani]

Would be nice to save the filename of the grid file too, but that looks like a faff at the moment. Hopefully it might be easier after the I/O refactor...

Also would be nice to save the hypnotoad_inputs and hypnotoad_input_geqdsk_file_contents but they're saved as string variables so not currently accessible through Mesh::get(). The reason for not saving them as attributes is that they are very long strings, so they clutter up the output of ncdump -h gridfile.nc. Any opinions on whether it's better to just make them attributes anyway, or to wait or the I/O refactor, when hopefully it will be possible to read and save them more easily?

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[ZedThree]

Probably wait for the I/O refactor? Hopefully won't be too long. Although I guess that doesn't help for the backport.

It also looks like it should be possible to make Mesh::get read string variables and fallback to getting from an attribute if not? Something like this maybe?

bool GridFile::get(Mesh *UNUSED(m), std::string &sval, const std::string &name, const std::string& def) {
  Timer timer("io");
  TRACE("GridFile::get(std::string)");
  
  if (!file->is_valid()) {
    throw BoutException("File cannot be read");
  }
  
  // Try to read from a variable first, maximum of 2048 characters
  constexpr int max_string_size = 2048;
  std::string temp_var;
  temp_var.reserve(max_string_size);
  const bool success_var = file->read(&(*temp_var.begin()), name, max_string_size);
  if (success_var) {
    sval = std::move(temp_var);
    return success_var;
  }

  const bool success = file->getAttribute("", name, sval);
  if (!success) {
    sval = def;
  }

  print_read_option(sval, name, filename, success);

  return success;
}

Not quite I suppose because max_string_size should be the exact size of the string to read. There's DataFormat::getSize, but I'm not sure that does exactly what we want here.

[ZedThree]

Just to note that when we get the new I/O stuff in, we won't need to have these as class members

[johnomotani]

Probably wait for the I/O refactor?

I think that's best. What's here is good enough for now, and I don't think it's worth putting more work into modifying Datafile GridFile, etc.