Fix ProgressPrinter test phase counter and add regression test

[gmartini2019]

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What does this PR do ?

Fixes a bug in the ProgressPrinter callback where validation-specific state was incorrectly referenced during the test phase, causing trainer.test() to crash when no validation loop had run.

Collection: Lightning / PyTorch callbacks

Changelog

• Fix incorrect usage of self.total_validation_steps during the test phase.
• Replace validation-specific counter with self.total_test_steps in on_test_batch_end.
• Add a CPU-only regression test to ensure trainer.test() does not crash when using ProgressPrinter.
• Mock Megatron microbatch logic in the test to avoid reliance on Megatron runtime initialization.

Usage

No changes are required from the user side. The fix is internal and ensures that the ProgressPrinter callback works correctly during trainer.test().

from nemo.lightning.pytorch.callbacks import ProgressPrinter
from lightning.pytorch import Trainer

trainer = Trainer(
    callbacks=[ProgressPrinter()],
)

trainer.test(model)

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Additional Information

• Related to # (issue)