test(queue/sql): add comprehensive e2e integration tests (#35)

## Summary
## Why?
                                                        
The SQL queue implementation needs comprehensive integration testing
against real MySQL to verify production-like behavior including message
workflows, partition management, retries, DLQ
handling, and consumer group coordination.

  ## What?

- Add 15 e2e integration tests using testcontainers-go covering: basic
ops, partitions, visibility timeout, retries, DLQ, concurrency, crash
recovery, and consumer groups
- Refactor test infrastructure: extract MySQL utilities to
`testutil/mysql.go` for reusability across test suites
- Add `integration_tests/queue/README.md` documenting test coverage and
running instructions

## Test Plan
`bazel test //integration_tests/queue:queue_test`

## Issues

Author: behinddwalls

integration_tests/BUILD.bazel

@@ -5,7 +5,6 @@ load("@rules_go//go:def.bzl", "go_test")
 go_test(
     name = "integration_test",
     srcs = [
-        "mysql.go",
         "servers.go",
         "suite_test.go",
     ],
@@ -18,6 +17,7 @@ go_test(
     ],
     tags = ["integration"],
     deps = [
+        "//integration_tests/testutil",
         "//gateway/protopb",
         "//orchestrator/protopb",
         "//speculator/protopb",

integration_tests/mysql.go

@@ -0,0 +1,25 @@
+load("@rules_go//go:def.bzl", "go_test")
+
+go_test(
+    name = "queue_test",
+    srcs = ["queue_test.go"],
+    data = [
+        "//extensions/queue/sql/schema",
+    ],
+    tags = ["integration"],
+    deps = [
+        "//entities/queue",
+        "//extensions/queue",
+        "//extensions/queue/sql",
+        "//integration_tests/testutil",
+        "@com_github_go_sql_driver_mysql//:mysql",
+        "@com_github_stretchr_testify//assert",
+        "@com_github_stretchr_testify//require",
+        "@com_github_stretchr_testify//suite",
+        "@com_github_testcontainers_testcontainers_go//:testcontainers-go",
+        "@com_github_testcontainers_testcontainers_go//network",
+        "@com_github_testcontainers_testcontainers_go_modules_mysql//:mysql",
+        "@com_github_uber_go_tally_v4//:tally",
+        "@org_uber_go_zap//zaptest",
+    ],
+)