ops functions cannot see write guards, value caches or preset hooks of a wrapper #3

Follow-up from the adversarial review of #2 (fix for #1).

The free functions in cosmodol.ops (replace_item, batch_items, delete_container, ...) resolve keys through every wrapping layer (_id_of_key), values through _data_of_obj, and, since #2, check k in store through the outer store before acting on an existing resource (so filt_iter scopes are honoured). Three things a function still cannot see, all documented in the cosmodol/ops.py module docstring:

1. Write guards: a layer whose own __setitem__/__delitem__ refuses (a read-only wrapper) is bypassed.
2. Value caches: cache_vals-style layers keep the pre-write value after replace_item/batch_items.
3. Key-aware preset= hooks (wrap_kvs(preset=...)) are not applied to replace_item/batch_items values; returned documents are in stored (leaf) form.
4. Creating operations (batch create/upsert, add_container, add_database) cannot consult a scope filter, since the key does not exist yet.

None of these is a regression (the old methods bypassed all of them too). Options: refuse when any layer overrides __setitem__/__delitem__ beyond dol.base.Store and is not a known-transparent dol wrapper (but filt_iter/cached_keys override them too, and the prefix-view pattern needs them); or wait for dol's is-a wrapping direction (i2mint/dol discussion #86), which would make methods correct again.