Implement load_into for SharedPtrDataLoader and add test (#11562)

[Tanish2101]

Summary:
Implemented the load_into method for SharedPtrDataLoader to support copying preallocated buffer data into a target buffer. This enables use cases where mutable model state has a meaningful initial value (e.g., on-device training or serialized read-before-write data).

Fixes
Fixes #11562

Test plan:
Added a unit test in shared_ptr_data_loader_test.cpp to verify that load_into():

1. Copies the correct data for valid offset/size.
2. Fails properly on invalid requests (e.g., out-of-bounds reads).

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/11707

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❌ 6 New Failures

As of commit fea2310 with merge base 56392aa ():

NEW FAILURES - The following jobs have failed:

• Lint / lintrunner / linux-job (gh)
  RuntimeError: Command docker exec -t daacfde83756d6f58298c0d7769583de1fb9429e037370c92fbdda152d7fba48 /exec failed with exit code 127
• pull / unittest / linux / linux-job (gh)
  /pytorch/executorch/extension/data_loader/test/shared_ptr_data_loader_test.cpp:174:25: error: no member named 'OutOfBounds' in 'executorch::runtime::Error'
• pull / unittest / macos / macos-job (gh)
  /Users/ec2-user/runner/_work/executorch/executorch/pytorch/executorch/extension/data_loader/test/shared_ptr_data_loader_test.cpp:174:25: error: no member named 'OutOfBounds' in 'executorch::runtime::Error'
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  RuntimeError: Command docker exec -t 64fa247090923f6040cd48dd2332d90d44a097537279eacde6e1aeba6cb408f8 /exec failed with exit code 1
• pull / unittest-editable / linux / linux-job (gh)
  /pytorch/executorch/extension/data_loader/test/shared_ptr_data_loader_test.cpp:174:25: error: no member named 'OutOfBounds' in 'executorch::runtime::Error'
• pull / unittest-editable / macos / macos-job (gh)
  /Users/ec2-user/runner/_work/executorch/executorch/pytorch/executorch/extension/data_loader/test/shared_ptr_data_loader_test.cpp:174:25: error: no member named 'OutOfBounds' in 'executorch::runtime::Error'

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[Tanish2101]

@pytorchbot label "release notes: none"

[Tanish2101]

Hi @JacobSzwejbka, I created a PR for this issue. This is the first time I am contributing to executorch. Please Let me know if there are any changes required.

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[mergennachin]

Hi @Tanish2101

Thank you for the contribution. Looks like @keyprocedure has started the PR for the same task (#11654)

[Tanish2101]

I have implemented the load_into() function for shared_ptr data loader so the implementation done by @keyprocedure for mmap data loader is sufficient? means there is no need for seperate implementation for shared_ptr ?

@mergennachin

[Tanish2101]

So now what should I do? means should I close the pull request which I have created for this issue? Let me know @mergennachin

[JacobSzwejbka]

Can you merge the declaration and implementation?