Slice 6: Migrate mutation .inner call sites to ObjectStore methods

Parent PRD

#7331

What to build

Replace direct internal mutation uses of object_store.inner with Lance ObjectStore methods that preserve Lance semantics. Per the parent's .inner tracker, this covers inner.delete, inner.copy, inner.delete_stream, inner.put_opts, inner.rename. Add rename / streaming-delete methods to the Lance store if missing.

Done per-module in focused PRs; the parent issue's call-site checklist tracks progress (dataset/mem_wal, lance-table/io/commit, namespace-impls/dir). Resolves Open Q4 application (copy/rename as store-level vs reader/writer ops) per the decision recorded in Slice 1.

Acceptance criteria

• Lance ObjectStore exposes methods covering every migrated mutation pattern (delete, copy, rename, streaming delete)
• Mutation .inner call sites outside lance-io plumbing migrated; parent checklist updated
• Remaining intentional .inner mutations documented as compatibility/plumbing
• Tests assert wrapper observability for migrated mutations (delete/copy/rename on a wrapped store)

Blocked by

• Blocked by #7332

Design sections addressed

• Phase 4 (Replace Internal .inner Call Sites) — mutation paths

Start with parent #7331's .inner tracker and the dependency on #7332, then review the listed dataset/mem_wal, lance-table/io/commit, and namespace-impls/dir call sites. Use the Slice 1 decision to resolve copy/rename ownership, and verify that migrated delete, copy, and rename paths expose wrapper observability while documenting intentional compatibility or plumbing uses.