Support normal-topic consumption with the gRPC SimpleConsumer

### Search before asking

- [X] I had searched in the [issues](https://github.com/apache/rocketmq-flink/issues) and found no similar issues.

### Motivation

The gRPC connector added in #135 / #136 only supports the LITE consumption model: the source binds a
**main lite topic** through `LiteSimpleConsumer` and defers acknowledgement to a downstream operator,
which is what enables fair per-sub-topic throttling.

That leaves the most common case uncovered: consuming a **plain normal topic** over gRPC. Users who
just want `topic + tag/SQL92 filter` today have to either fall back to the remoting connector or
model their topic as a lite topic, and they inherit a downstream ack operator they do not need.

### Solution

Add a SIMPLE consumption mode alongside LITE, selected by a single `rocketmq.source.mode`
(SQL: `source.mode`) option:

- Subscribe one normal topic through the SDK `SimpleConsumer` with an optional tag / SQL92 filter
expression.
- Acknowledge on the source side, aligned with checkpoints — the same approach the GCP Pub/Sub
connector uses: receipt handles of emitted records are grouped per checkpoint and acked from
`notifyCheckpointComplete`, giving at-least-once. Un-acked messages are redelivered once their
invisible duration expires.
- Issue those acks through the very consumer that received the messages, so no second gRPC
connection and no downstream ack operator are involved.
- Abstract the two SDK Pop clients (`SimpleConsumer` / `LiteSimpleConsumer`) behind one internal
interface, since they expose the same receive / ack / changeInvisibleDuration operations but share
no common type.
- Expose the mode and the filter options through the SQL connector as well.

LITE remains fully supported for the lite-topic + downstream-throttling scenario.

### Are you willing to submit a PR?

- [X] I'm willing to submit a PR!

Start by tracing the existing gRPC LITE source from LiteSimpleConsumer through checkpoint completion and the SQL connector’s source.mode exposure. Compare the GCP Pub/Sub connector’s notifyCheckpointComplete acknowledgement flow, then verify SIMPLE receives filtered normal-topic messages, acks through the same consumer, and leaves LITE behavior intact.

Written by the indexing model from the issue text.