[Bug] Scan from-snapshot-full and compact-full won't produce a snapshot in streaming mode with LogStore when start up

### Search before asking

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

### Paimon version

0.5-release

### Compute Engine

flink

### Minimal reproduce step

1. set log store
2. set scan.mode = 'from-snapshot-full' or 'compacted-full'
3. set streaming-read-mode = log
4. streaming scan the table

### What doesn't meet your expectations?

In FlinkSourceBuilder#build(), there won't produce from the start snapshot on the table upon first startup, it will read the log directly. Which is unexpected.

### Anything else?

_No response_

### Are you willing to submit a PR?

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

Start in FlinkSourceBuilder#build() and reproduce the listed setup with a LogStore, streaming-read-mode set to log, and scan.mode set to from-snapshot-full or compacted-full. Trace the startup scan path and verify that an initial table snapshot is produced before log records are read in both modes.

Written by the indexing model from the issue text.