Registry: Add Store class to support multiple Registry backends

[AgentDosaku]

Summary

This PR implements a new Store abstraction that wraps multiple Registry instances behind one API.

What was added

• Store and StoreMount implementation:
  • mindtrace/registry/mindtrace/registry/core/store.py
• New Store-specific exceptions:
  • StoreLocationNotFound
  • StoreKeyFormatError
  • StoreAmbiguousObjectError
• Public exports from mindtrace.registry for Store classes/exceptions.
• Config support for default Store local path:
  • MINDTRACE_DIR_PATHS.STORE_DIR
  • default in config.ini: ${MINDTRACE_DIR_PATHS:ROOT}/store
• Unit tests for Store behavior:
  • tests/unit/mindtrace/registry/core/test_store.py
• Design document:
  • docs/storage/store-design.md

Implemented behavior

• Store() defaults to a local mount (default) backed by config-driven STORE_DIR.
• load("name") (unqualified) performs cross-mount discovery.
• load("location/name") (qualified) only checks the specified mount.
• If unqualified load finds multiple matches, raises StoreAmbiguousObjectError listing locations.
• Local name→location cache is used to prioritize discovery probes.
• save and delete require qualified keys (<location>/<name>) to prevent accidental writes/deletes.

Design Doc

• docs/storage/store-design.md

Reviewer copy/paste examples

1) Two local registries + explicit writes

from pathlib import Path
from mindtrace.registry import Registry, Store

r1 = Registry(backend=Path("/tmp/store_a"), version_objects=True, mutable=True)
r2 = Registry(backend=Path("/tmp/store_b"), version_objects=True, mutable=True)

store = Store(mounts={"a": r1, "b": r2}, default_location="a")

store.save("a/model:resnet", {"acc": 0.92})
store.save("b/model:vit", {"acc": 0.95})

print(store.load("a/model:resnet"))
print(store.load("b/model:vit"))

2) Unqualified load discovery

from pathlib import Path
from mindtrace.registry import Registry, Store

r1 = Registry(backend=Path("/tmp/store_a"), version_objects=True, mutable=True)
r2 = Registry(backend=Path("/tmp/store_b"), version_objects=True, mutable=True)

store = Store(mounts={"a": r1, "b": r2})
store.save("b/data:item1", "hello")

# No location specified -> Store checks mounts and finds b/data:item1
print(store.load("data:item1"))

3) Ambiguity handling

from pathlib import Path
from mindtrace.registry import Registry, Store
from mindtrace.registry.core.exceptions import StoreAmbiguousObjectError

r1 = Registry(backend=Path("/tmp/store_a"), version_objects=True, mutable=True)
r2 = Registry(backend=Path("/tmp/store_b"), version_objects=True, mutable=True)

store = Store(mounts={"a": r1, "b": r2})
store.save("a/shared:item", 1)
store.save("b/shared:item", 2)

try:
    store.load("shared:item")
except StoreAmbiguousObjectError as e:
    print("Ambiguous as expected:", e)

# explicit location works
print(store.load("a/shared:item"))

4) Default local Store with no mounts provided

from mindtrace.registry import Store

store = Store()  # creates location="default" at MINDTRACE_DIR_PATHS.STORE_DIR
store.save("default/demo:item", {"ok": True})
print(store.load("default/demo:item"))

Testing

• pytest -q tests/unit/mindtrace/registry/core/test_store.py
• ds test --unit

Closes #279