Phase 5 Slice 12 (backlog#939): move the local disk registry — the
path->disk map, the disk-id->endpoint map, and the pool/set/drive layout —
out of the three GLOBAL_LOCAL_DISK_* process statics into the per-instance
InstanceContext.
This is the migration the owned-guard prerequisite (#4501) unblocked.
- InstanceContext gains three `Arc<RwLock<..>>` registry fields, constructed
eagerly (empty), plus pub(crate) handle accessors.
- The three runtime-source handle functions (`local_disk_map_handle` etc.) now
return the current instance's registry via `current_ctx()`; every direct
`GLOBAL_LOCAL_DISK_*` access in runtime::sources (~15 sites) routes through
those handles instead. Accessors that hold a write guard across `.await`
(`record_local_disks`, `initialize_local_disk_maps`, `replace_local_disk_id`)
bind the handle first, so the same locks are held across the same awaits.
- The three statics are removed; the test-reset helper clears the current
context's registry.
Construction window: the registry is populated during storage startup, before
the ECStore exists, via the bootstrap context that `ECStore::new` then adopts —
so startup writes and post-construction reads share one registry (no
split-brain). Single-instance behavior is byte-for-byte unchanged; the
GLOBAL_LOCAL_DISK_* boundary arch guard passes with the statics gone.
Verification: cargo test -p rustfs-ecstore (32 disk/instance tests green) and
-p rustfs-heal (201 green), cargo clippy -p rustfs-ecstore -p rustfs-heal
--all-targets (clean), make pre-commit (pass).
Refs: backlog#939 (Phase 5, Slice 12; disk-registry migration)
