[Stream][Binlog] Override scan-state comparison for OlapStreamScan

### Description

While reviewing PR #65472, I found that `LogicalOlapTableStreamScan` has stream-specific state that is relevant to scan equivalence, especially `StreamReadMode` (`INCREMENTAL`, `SNAPSHOT`, and `RESET`). The class includes `readMode` in `equals()`, but it does not provide a stream-specific `hasSameScanState()` override.

After PR #65472 makes scan-state comparison relevant to plan rewrites such as `PullUpJoinFromUnionAll`, two stream scans may be compared through the generic OLAP scan-state logic without explicitly checking stream-specific state. If scans with different stream read modes are treated as equivalent, a rewrite could reuse or merge a scan with different stream semantics.

### Requested follow-up

Please add an override for `hasSameScanState()` in `LogicalOlapTableStreamScan` (or the corresponding `OlapStreamScan` abstraction) and include all stream-specific state that affects execution. Add FE unit tests covering:

- equal stream scans with the same read mode;
- different read modes;
- any selected-partition or stream-lowering state that must participate in scan equivalence.

This is a source-level follow-up to [PR #65472](https://github.com/apache/doris/pull/65472). The direct stream/binlog runtime impact still needs an end-to-end reproduction; this issue is opened to ensure the missing override and its contract are resolved explicitly.

**上面这个PR 会先pick 到4.1 分支，但是4.1分支现在不支持stream， 所以要等后面4.1支持了stream之后， 再单独pick stream scan的overrite 到4.1 分支上**

Related tracking issues:

- [#65265](https://github.com/apache/doris/issues/65265)
- [#65418](https://github.com/apache/doris/issues/65418)

Start with LogicalOlapTableStreamScan and the generic hasSameScanState() implementation, then compare its stream-specific state with the existing equals() logic. Add FE unit tests for matching and differing StreamReadMode values, plus selected-partition or stream-lowering state identified during the review. Done means stream scans with different execution state are not considered equivalent.

Written by the indexing model from the issue text.