[ISSUE #5231#5232#5233] Harden ConnectorRuntime against data loss; split connector-api SPI module; add plugin unit tests (#4642)

[qqeasonchen]

Motivation

Connector plane hardening batch — three P0/P1 items from the connector review (#5296 follow-up):

1. P0 data-loss hardening (follow-up to [Bug] Using the HTTP connector, data cannot be saved to RocketMQ after being pushed. #5231 / [Bug] Using http connector in common protocol，data cant be saved in the topic #5232 / [Bug] http connector in common protocol has a json deserialization error #5233): those three bugs crashed the old openconnect framework (already removed by the uni-arch redesign); the crash classes (SourceWorker, RecordOffsetManagement, CommonProtocol) no longer exist. But the failure mode — one bad event killing the loop and silently stranding the rest of the batch — could still happen in the new ConnectorRuntime. This PR closes that class of bugs:

   • runSourceOnce(): per-event isolation — a publish that throws (bad CloudEvent, broken URL) is logged + skipped + counted; the rest of the batch still publishes; null events in a poll() batch are skipped, not NPE.
   • runSinkOnce(): per-delivery ACK isolation — one ACK failure no longer loses the remaining ACKs/offset; EventMesh re-delivers.
   • offsetStore.put() failures no longer abort the publish/commit path (checkpoint lost is logged, event flow continues).
   • getSourcePublishFailures() counter exposes skipped events to the admin API.

2. P1 connector-api module split (plan doc included at docs/contrib/connector-api-split-plan.md): the 7 SPI interfaces (SourceConnector, SinkConnector, EventMeshEndpoint, HttpCaller, ConnectorOffsetStore, CloudEventSerializer, PollEntry) move from eventmesh-connector-runtime into a new :eventmesh-connector-api module (deps: cloudevents-core only). The package name stays org.apache.eventmesh.connector, so all 23 plugins keep their imports — only their build.gradle dependency swaps. Enforcement is two-layer:

   • compile-time: plugins no longer have the runtime on their classpath;
   • ArchUnit: new ruleConnectorPluginsDependOnlyOnSpi (FAIL mode, extends [Architecture Review][P2] Gradle dependency guardrails (architectureCheck) #5305 guard) + a canary negative test proving the rule fires.

3. P0 plugin unit tests ([Unit Test] Add unit test for eventmesh-connector-file module #4642 follow-up): first tests ever for connector-file (5+5), connector-kafka (1, Kafka MockProducer), connector-pulsar (2, smoke), connector-rocketmq (3, smoke). File connectors gain close*Quietly() so tests release file handles on Windows.

Also: eventmesh.properties gains a commented Connector Runtime section; dist-connector packaging ships the api jar in apps/ next to the runtime jar.

Modifications

• eventmesh-connector-api/ — new module: 7 SPI interfaces + package-info
• eventmesh-connector-runtime/ — SPI files removed; api project(':eventmesh-connector-api') dependency; ConnectorRuntime hardening + 4 new tests
• 23 × eventmesh-connector-plugin/*/build.gradle — dep swap runtime → api
• eventmesh-architecture-guard/ — new rule + canary test (11/11 green)
• build.gradle (root) — dist-connector ships api jar
• eventmesh-runtime/conf/eventmesh.properties — connector section
• eventmesh-connector-plugin/eventmesh-connector-{file,kafka,pulsar,rocketmq}/src/test/ — new tests

Documentation

• docs/contrib/connector-api-split-plan.md — split rationale, migration steps (M1/M2/M3), risks, acceptance criteria

Verifying this patch

Local (JDK 21, Windows): :eventmesh-connector-api:build, :eventmesh-connector-runtime:build, :connector-{file,kafka,pulsar,rocketmq}:build (incl. checkstyle), :eventmesh-runtime:compileJava, :eventmesh-architecture-guard:test 11/11 — all green. 33 new/updated unit tests total (17 runtime + 16 plugin).