[to dev/1.3] Fix tree model WAL serialized sizes

[Caideyipi]

Cherry-picks the tree-model relevant parts of ab887eb (#17867) to dev/1.3.

Included:

• Fix WAL string serialized-size calculations for tree delete/insert nodes and measurement schemas.
• Fix partial InsertTablet WAL entry size calculation on dev/1.3's tablet start/end path.
• Fix legacy tree Deletion serialized size and add coverage for non-ASCII paths.

Validation:

• mvn spotless:apply -pl iotdb-core/datanode
• git diff --check
• Attempted targeted datanode tests, but the module currently fails during main compilation before test execution with existing pipe/schema API mismatches unrelated to these changed files.