Add more information to the log on the current stage

[gregtatum]

We're using OpusTrainer in Firefox Translations, and I was finding some of the OpusTrainer behavior confusing. This PR adds some more logs to explain a bit more what is going on.

Example output:

[2024-09-13 15:46:33] [Trainer] [INFO] Starting stage: "train"
[2024-09-13 15:46:33] [Trainer] [INFO] Running until dataset "original" for 1 epoch(s)
[2024-09-13 15:46:33] [Trainer] [INFO] Using curriculum modifiers:
[2024-09-13 15:46:33] [Trainer] [INFO]  - UpperCaseModifier (0.07)
[2024-09-13 15:46:33] [Trainer] [INFO]  - TitleCaseModifier (0.05)
[2024-09-13 15:46:33] [Trainer] [INFO]  - TypoModifier (0.05)
[2024-09-13 15:46:33] [Trainer] [INFO]  - NoiseModifier (0.0005)
[2024-09-13 15:46:33] [Trainer] [INFO] Reading original for epoch 0
[2024-09-13 15:46:34] [Trainer] [INFO] Reading original for epoch 1
[2024-09-13 15:46:34] [Trainer] [INFO] Finished the last stage
[2024-09-13 15:46:34] [Trainer] [INFO] waiting for trainer to exit. Press ctrl-c to be more aggressive

[gregtatum]

Ah, just noticed this has a log test which fails.

[gregtatum]

Ok, the tests pass now.

➤ ./run-tests.sh
.......................................................
----------------------------------------------------------------------
Ran 55 tests in 8.557s

[jelmervdl]

Thank you!