pw_log_tokenized: Update Python Metadata fields

- Update the field order in pw_log_tokenized.Metadata to match the order
  in C++ (level, line, flags, module).
- Update the pw_log_tokenized.Metadata class and add tests.

Change-Id: I6c7ecdad94bc7d55bde11731958cef76ff2e648c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/48361
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>