feat(stovepipe): add storage extension with RequestStore + RequestURIStore (MySQL) (#277)

## Summary
### Why?

The ingest controller (PR #276) mints a `Request` but is log-only. For
the pipeline to do real work it needs to persist requests and look them
up two ways, both flowing from the workflow RFC: by **request ID**
(every downstream stage reloads the entity), and by **(queue, commit
URI)** to find whether a commit is already being validated — the RFC's
`(Queue, head URI)` dedup key.

### What?

A new `stovepipe/extension/storage` extension plus its first backend
(MySQL), mirroring the SubmitQueue storage conventions: a factory
`Storage` interface,
`ErrNotFound`/`ErrAlreadyExists`/`ErrVersionMismatch` sentinels,
metrics-wrapped MySQL ops, and optimistic-locking CAS with version
arithmetic owned by the caller.

Two stores, **one per table**:

- **`RequestStore`** (`request` table) — `Create` (ErrAlreadyExists on
dup ID); `Get` by ID (ErrNotFound); `Update`, a pure conditional write
taking the whole `Request` plus `oldVersion`/`newVersion`, persisting
the mutable fields (uri, state) only if the stored version matches (else
ErrVersionMismatch).
- **`RequestURIStore`** (`request_uri` table) — the reverse index from a
validated commit to its request, keyed by `(queue, uri)`: `Create`
(ErrAlreadyExists on a duplicate `(queue, uri)` — the dedup signal) and
`GetIDByURI` (ErrNotFound). It's a separate store because it's a
separate table; the two are written independently (no cross-table
transaction) so the contract stays satisfiable by key/value backends.

Ships the MySQL impl, schema (`request.sql`, `request_uri.sql`),
generated mocks, and a docker-compose integration test.

Follow-ups: wire `storage` into `ingest` (dedup via `GetIDByURI`, then
`Create`); an in-memory backend + shared contract suite.

## Test Plan
- ✅ `bazel test
//test/integration/stovepipe/extension/storage/mysql:mysql_test` — real
MySQL via docker-compose: create/get/update-CAS (success, stale-version
mismatch, missing-row mismatch), not-found, duplicate-ID, and the URI
mapping (round-trip, not-found, duplicate dedup, per-queue isolation).
- ✅ `bazel build //stovepipe/...`; `make check-gazelle`, `make
check-tidy`, `make lint` clean. Mocks regenerated and idempotent.

## Issues


## Stack
1. #276
1. @ #277
1. #278
1. #279

Author: behinddwalls

stovepipe/extension/storage/BUILD.bazel

@@ -0,0 +1,13 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "storage",
+    srcs = [
+        "request_store.go",
+        "request_uri_store.go",
+        "storage.go",
+    ],
+    importpath = "github.com/uber/submitqueue/stovepipe/extension/storage",
+    visibility = ["//visibility:public"],
+    deps = ["//stovepipe/entity"],
+)

stovepipe/extension/storage/mock/BUILD.bazel

@@ -0,0 +1,17 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "mock",
+    srcs = [
+        "request_store_mock.go",
+        "request_uri_store_mock.go",
+        "storage_mock.go",
+    ],
+    importpath = "github.com/uber/submitqueue/stovepipe/extension/storage/mock",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//stovepipe/entity",
+        "//stovepipe/extension/storage",
+        "@org_uber_go_mock//gomock",
+    ],
+)

stovepipe/extension/storage/mock/request_store_mock.go

@@ -0,0 +1,19 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "mysql",
+    srcs = [
+        "request_store.go",
+        "request_uri_store.go",
+        "storage.go",
+    ],
+    importpath = "github.com/uber/submitqueue/stovepipe/extension/storage/mysql",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//platform/metrics",
+        "//stovepipe/entity",
+        "//stovepipe/extension/storage",
+        "@com_github_go_sql_driver_mysql//:mysql",
+        "@com_github_uber_go_tally//:tally",
+    ],
+)