[Load] Handle empty path nodes during database auto-creation

[Caideyipi]

Description

A tree-model TsFile may contain a segmented device ID with an empty path node, for example root. represented as ["root", ""]. LOAD previously copied those segments into a PartialPath without structural validation and could derive an invalid root. database path.

Clusters affected by the old behavior may already contain such a legacy root. database. When LOAD listed existing databases, the previous string-prefix check treated valid candidates such as root.sg as covered by root., skipped their creation, and could make ordinary TsFiles fail to load.

This PR:

• validates every device node before LOAD queries ConfigNode or attempts database auto-creation, so null or empty nodes fail locally with a clear illegal-path error;
• ignores malformed legacy database names returned by ConfigNode when filtering databases to create, allowing ordinary TsFiles to load even if root. already exists;
• compares database relationships by path nodes instead of raw string prefixes, so names such as root.sg and root.sg1 are not incorrectly treated as ancestors of one another.

The ConfigNode-wide guard that prevents new database paths with empty nodes is handled separately in #18308.

Tests

• mvn spotless:apply -pl iotdb-core/datanode
• LoadTsFileAnalyzerTest compiled against the current module dependencies and run with JUnitCore (7 tests passed).
• The normal DataNode Maven lifecycle is currently blocked locally by unrelated stale generated Freemarker sources and SNAPSHOT dependency mismatches.

This PR has:

• been self-reviewed.
• added unit tests to cover the new code paths.

Key changed/added class

• TreeSchemaAutoCreatorAndVerifier