Bugfix in TosaSpecification representation

[per]

Fix up TOSA 1.0 class string representation handling and add test cases for the fixed functionality.

Test plan

Tests added to unit tests.

cc @digantdesai @freddan80 @zingo @oscarandersson8218

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/8137

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❌ 1 New Failure, 2 Cancelled Jobs

As of commit 224c96f with merge base 3eea1f1 ():

NEW FAILURE - The following job has failed:

• trunk / test-llama-runner-mac (bf16, portable) / macos-job (gh)
  RuntimeError: mmap can only be used with files saved with torch.save(stories110M.pt, _use_new_zipfile_serialization=True), please torch.save your checkpoint with this option in order to use mmap.`

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / test-eval_llama-mmlu-linux / linux-job (gh)
  ##[error]The operation was canceled.
• pull / test-llava-runner-linux / linux-job (gh)
  ##[error]The operation was canceled.

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[zingo]

Tests fails unrelated