Module deep-copies LoadBackendOptionsMap on load (#19673)

[metascroy]

Summary:

Module::load(LoadBackendOptionsMap&, ...) previously stored a raw
const-pointer to the caller's map (backend_options_), forcing every
caller (and every language binding) to keep the input map and its
backing BackendOption arrays alive past the load() call to keep lazy
load_method invocations safe. That contract is hard to express across
language boundaries (it's the reason the Apple bindings carry an extra
ivar to retain the wrapper -- removed in a follow-up).

Replace the borrowed-pointer with a Module-owned copy:

• Module gains a (storage, owned map, has-flag) triple replacing the
  raw pointer. The storage is a vector-of-vectors that owns the
  BackendOption arrays; the owned map's Spans reference it.
• load(LoadBackendOptionsMap&, ...) deep-copies via the new
  LoadBackendOptionsMap::entry_at(i) accessor into a local
  (storage, map) pair, calls load_internal, and only commits to the
  members on success. Transactional rollback for free.
• load_method's fallback (when called with no explicit options) now
  reads the Module-owned map.

The signature of the public load(LoadBackendOptionsMap&, ...) overload
is unchanged; existing callers (XNNPACK runtime tests, dynamic_shim,
module_test) get the upgrade for free and may now release their
input map immediately after load() returns.

Reviewed By: shoumikhin

Differential Revision: D105100372

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/19673

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❗ 2 Active SEVs

There are 2 currently active SEVs. If your PR is affected, please view them below:

• Run pull request jobs on OSDC runners in shadow mode
• Rollout OSDC prod cluster in us-west-1

✅ No Failures

As of commit cba9369 with merge base f3387d0 ():
💚 Looks good so far! There are no failures yet. 💚

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[meta-codesync]

@metascroy has exported this pull request. If you are a Meta employee, you can view the originating Diff in D105100372.

[github-actions]

This PR needs a release notes: label

If your change should be included in the release notes (i.e. would users of this library care about this change?), please use a label starting with release notes:. This helps us keep track and include your important work in the next release notes.

To add a label, you can comment to pytorchbot, for example
@pytorchbot label "release notes: none"

For more information, see
https://github.com/pytorch/pytorch/wiki/PyTorch-AutoLabel-Bot#why-categorize-for-release-notes-and-how-does-it-work.