[miniflare] Add storage-owner tests and high-concurrency oracle

Unit tests for owner election, presence, routing and teardown, plus a high
-concurrency oracle that runs multiple instances against one persist root and
asserts KV/R2/D1/Streams/Secrets/Images sharing with exactly-correct results
under contention. The oracle runs under MINIFLARE_TEST_SHARED_OWNER (added to
turbo.json globalPassThroughEnv) so it gates both feature-on and baseline modes.

Author: penalosa

.changeset/shared-storage-owner.md

@@ -0,0 +1,9 @@
+---
+"miniflare": minor
+---
+
+Add experimental `unsafeSharedStorageOwner` option to share local storage across processes
+
+When several Miniflare instances run against the same persist root (for example multiple `wrangler dev` / `vite dev` sessions), each one opens the same SQLite and blob files, which can produce cross-process `SQLITE_BUSY` errors under concurrent access. With `unsafeSharedStorageOwner` enabled, a single detached "owner" process opens the storage files and every other instance routes its KV, R2, D1, Images, Streams and Secrets Store operations to that owner over the remote-bindings boundary, so exactly one process performs storage I/O. The owner is elected and spawned automatically, publishes its address to the persist root, and self-terminates once no instances remain.
+
+The option is off by default. Cache, Durable Objects and Workflows are intentionally kept per-instance rather than routed, so processes never contend on those databases.