Add SFT trainer and sft task

[jialei777]

Enable SFT, specifically:

• add sfttrainer and the associated unit test
• update dataset a bit for sft task
• update readme and e2e test

GSM8k training:

[2025-06-06 16:57:39,483][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Num replicas: 1
[2025-06-06 16:57:39,484][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Starting training
[2025-06-06 16:57:39,484][torchprime.torch_xla_models.trainer.base_trainer][INFO] -     Max step: 100
[2025-06-06 16:57:39,484][torchprime.torch_xla_models.trainer.base_trainer][INFO] -     Global batch size: 64
[2025-06-06 16:59:53,697][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.0000, step: 0, loss: 1.2016, lr: 4.00e-06, trace time: 132096.80 ms
[2025-06-06 17:02:07,179][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.0431, step: 5, loss: 1.5330, lr: 2.40e-05, trace time: 1018.20 ms
[2025-06-06 17:02:12,027][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.0862, step: 10, loss: 3.3264, lr: 3.96e-05, trace time: 734.19 ms
[2025-06-06 17:02:16,878][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.1293, step: 15, loss: 1.5569, lr: 3.73e-05, trace time: 1108.31 ms
[2025-06-06 17:02:21,727][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.1724, step: 20, loss: 0.7388, lr: 3.51e-05, trace time: 740.09 ms
[2025-06-06 17:02:26,580][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.2155, step: 25, loss: 0.6763, lr: 3.29e-05, trace time: 736.51 ms
[2025-06-06 17:02:31,460][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.2586, step: 30, loss: 0.5993, lr: 3.07e-05, trace time: 735.40 ms
[2025-06-06 17:02:36,287][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.3017, step: 35, loss: 0.5973, lr: 2.84e-05, trace time: 735.46 ms
[2025-06-06 17:02:41,140][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.3448, step: 40, loss: 0.5832, lr: 2.62e-05, trace time: 735.81 ms
[2025-06-06 17:02:45,992][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.3879, step: 45, loss: 0.5754, lr: 2.40e-05, trace time: 739.57 ms
[2025-06-06 17:02:50,846][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.4310, step: 50, loss: 0.5350, lr: 2.18e-05, trace time: 736.22 ms
[2025-06-06 17:02:55,701][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.4741, step: 55, loss: 0.5491, lr: 1.96e-05, trace time: 1111.88 ms
[2025-06-06 17:03:00,554][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.5172, step: 60, loss: 0.4939, lr: 1.73e-05, trace time: 738.59 ms
[2025-06-06 17:03:05,407][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.5603, step: 65, loss: 0.5829, lr: 1.51e-05, trace time: 736.64 ms
[2025-06-06 17:03:10,261][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.6034, step: 70, loss: 0.5455, lr: 1.29e-05, trace time: 741.68 ms
[2025-06-06 17:03:15,116][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.6466, step: 75, loss: 0.5600, lr: 1.07e-05, trace time: 746.14 ms
[2025-06-06 17:03:19,972][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.6897, step: 80, loss: 0.5516, lr: 8.44e-06, trace time: 741.00 ms
[2025-06-06 17:03:24,826][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.7328, step: 85, loss: 0.5162, lr: 6.22e-06, trace time: 742.01 ms
[2025-06-06 17:03:29,685][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.7759, step: 90, loss: 0.5052, lr: 4.00e-06, trace time: 742.07 ms
[2025-06-06 17:03:34,540][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Epoch: 0.8190, step: 95, loss: 0.5012, lr: 1.78e-06, trace time: 740.57 ms
[2025-06-06 17:03:38,423][torchprime.torch_xla_models.trainer.base_trainer][INFO] - Finished training run
[2025-06-06 17:03:38,424][torchprime.torch_xla_models.trainer.base_trainer][INFO] - ***** train metrics *****

[tengyifei]

Hmm, very strange. Latest SFT run (https://github.com/AI-Hypercomputer/torchprime/actions/runs/15501248395/job/43649488239?pr=284) is taking forever to finish. Looks like it is compiling many graphs. In the past I've seen this happening when there are unexpected transfers from the TPU to the CPU (e.g. printing or calling .cpu()).

[jialei777]

@tengyifei Error is due to the export model in the end (so align with transfers from the TPU to the CPU as you mentioned). I don't know why, seems it worked with tpu vm. Any idea on how to debug this?

[yaoshiang]

I get a lot of notifications for this PR and it's also getting large. Can you work on smaller PRs that chain towards a bigger change, and, ask for more intermediate reviews? with unit tests, it's pretty easy to introduce small PRs that are 100 lines of code. https://google.github.io/eng-practices/review/developer/small-cls.html

[yaoshiang]

Please create a PR when ready for review, and make the PRs small - 100 lines of code is a good target. A PR that lives for days with 18 commits (not addressing comments) is getting too large.