fix(core): report dropped entities and restore the cache on error

[LukasGold]

Fixes #183. Two independent gaps in src/osw/core.py.

Based on fix/175-store-entity-verify (#182), not on main, because the first change touches store_entity_, the same function #182 changes, and the new tests depend on the write verification it adds. GitHub retargets this PR to main once #182 merges.

1. store_entity_ no longer drops an entity silently

Two error paths logged and returned. A plain return is not an exception, so handle_upload_object_ returned normally, the collector loop at src/osw/core.py:2048-2052 recorded nothing, and the entity reached neither StoreEntityResult.pages nor StoreEntityResult.failed. store_entity then returned without raising StoreEntityPartialError, so the caller saw a successful call with fewer pages than entities passed in.

Both conditions now raise, so the existing collector loop records them:

• get_title(entity_) raises: ValueError, chained from the original exception
• namespace_ or title_ is None: TypeError, matching the neighbouring raise TypeError for a missing overwrite_class_param

The local _logger.error call in the first branch was removed, because the collector loop already logs every failed entity.

Behaviour change

An entity that met one of these two conditions previously caused no exception. It now contributes to StoreEntityResult.failed, which makes store_entity raise StoreEntityPartialError. A caller that depended on the silent drop will now see the error.

2. load_entity restores the page cache state in a finally block

The state was saved at the start and restored near the end, outside any try. An exception from the calls in between (get_page, get_slot_content, the category schema fetch, fetch_schema, namespace_from_full_title) left the cache in the state set for the load. That is the failure mode of #176: a later get_page can return a revision from before a write.

The body is now wrapped in try and the restore is in finally. Only indentation changed inside the body. ruff format rewrapped two lines that the extra indentation pushed past the line limit.

_fetch_schema had the same pattern and is fixed separately in #180.

Tests

• tests/test_store_entity_silent_drop.py, 6 tests: title failure reported in both the serial and the parallel path, missing namespace, missing title, a mixed batch where only the failing entity is reported, and a normal-path guard.
• tests/test_load_entity_cache_restore.py, 8 tests: the cache state survives an exception from get_page for both starting states, the same for an exception raised inside the per-page loop after get_page succeeded, plus normal-path guards.

Both files run offline. Reverting only the try/finally and rerunning tests/test_load_entity_cache_restore.py gives 4 failed, 4 passed. The four that fail are the two get_page cases with disable_cache=True and both page-loop cases. The other four cannot discriminate, because with disable_cache=False the cache is never changed at all.

The page-loop test exists because a test that only raises from get_page would still pass if the try covered just the first statement of the body.

Full unit suite: 231 passed.

Not addressed

load_entity has a separate pre-existing defect at src/osw/core.py:1222-1228: disable_cache=True sets the cache to the opposite of the caller's starting state instead of disabling it. Filed as #186. This PR keeps that behaviour unchanged.

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