[spark] improve streaming read support

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar.

### Motivation

This is umbrella issue to track spark streaming read support

### Solution

- startup mode
- read log table
- read primary key table
- rate limit

### Anything else?

_No response_

### Willingness to contribute

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

No files, tests, or entry points are named. Start by locating the existing Spark streaming read integration and separate the four requested areas: startup mode, log tables, primary-key tables, and rate limiting. Done means the listed streaming-read capabilities are implemented and verified.

Written by the indexing model from the issue text.