feat(storage): add raw binary-blob primitive to every storage adapter

Introduce a first-class binary-blob storage primitive on the StorageAdapter
contract and implement it across all storage backends. This stores opaque byte
payloads verbatim instead of base64-in-JSON, eliminating the ~33% inflation and
full-materialization cost of the JSON envelope. It unblocks zero-copy,
mmap-able column-store segments and batch vector I/O at billion scale.

New methods (declared abstract on BaseStorageAdapter, the class that implements
StorageAdapter, and added to the StorageAdapter interface):

  saveBinaryBlob(key, data)    raw write, atomic on real filesystems
  loadBinaryBlob(key)          exact bytes, or null if absent
  deleteBinaryBlob(key)        idempotent (missing is ignored)
  getBinaryBlobPath(key)       real local fs path where one exists, else null

Shared key -> location convention across every adapter: the key's
"/"-separated segments nest under a `_blobs/` prefix and are suffixed with
`.bin`, e.g. "graph-lsm/source/sstable-123" ->
"<root>/_blobs/graph-lsm/source/sstable-123.bin". Blobs are not branch-scoped
(COW): they are immutable producer-managed segments.

Per-adapter behavior:
- FileSystemStorage: writes under <rootDir>/_blobs via tmp+rename; returns the
  real on-disk path so native code can mmap it directly. Path convention matches
  the existing MmapFileSystemStorage subclass byte-for-byte.
- S3CompatibleStorage / R2Storage / GcsStorage / AzureBlobStorage: put/get/delete
  raw octet-stream objects; getBinaryBlobPath returns null (remote stores have no
  local path).
- MemoryStorage: defensive-copied Map<string, Buffer>; null path; cleared on
  clear().
- OPFSStorage: stores raw bytes in the OPFS tree; null path.
- HistoricalStorageAdapter: read-only — save/delete throw; load resolves the
  blob from the historical commit tree; null path.

Tests: tests/unit/storage/binaryBlob.test.ts exercises save/load round-trip
(byte-identical, incl. non-UTF8 bytes), overwrite, delete-then-load, load-missing,
and getBinaryBlobPath behavior for all eight adapters. Cloud adapters run against
in-memory client fakes that drive the real adapter code; OPFS runs against an
in-memory FileSystem Access API mock; the historical adapter commits a blob into
a real COW tree. 59 new tests; full unit suite (1398 tests) green.

src/storage/baseStorage.ts

@@ -2123,6 +2123,12 @@ export abstract class BaseStorage extends BaseStorageAdapter {
    */
   protected abstract listObjectsUnderPath(prefix: string): Promise<string[]>
 
+  // Raw binary-blob primitive (saveBinaryBlob/loadBinaryBlob/deleteBinaryBlob/
+  // getBinaryBlobPath) is declared abstract on BaseStorageAdapter — the class
+  // that `implements StorageAdapter` — alongside the other public storage
+  // methods. Each concrete adapter implements it. See BaseStorageAdapter for the
+  // contract and the shared `_blobs/<key>.bin` key→location convention.
+
   /**
    * Save metadata to storage (now typed)
    * Routes to correct location (system or entity) based on key format