Use NVARCHAR for Spring Batch SQL Server metadata

[Chienlin1014]

Spring Batch SQL Server metadata tables default to VARCHAR, but the Microsoft JDBC driver sends strings as NVARCHAR. This mismatch causes implicit conversions, slows queries, and increases deadlock risk.

Update schema-sqlserver.sql to use NVARCHAR for all string columns, aligning with the driver and improving performance.

fix #5064

[Chienlin1014]

reference： International features of the JDBC driver

[Chienlin1014]

Fixes #5064

[fmbenhassine]

@Chienlin1014 Thank you for reporting this issue and for contributing a PR! LGTM 👍

Can you please add a migration script for v6 similar to https://github.com/spring-projects/spring-batch/blob/a33f0e9a328b12c4042a20d577fd0d4460e5734b/spring-batch-core/src/main/resources/org/springframework/batch/core/migration/5.0/migration-sqlserver.sql that alters the tables and changes the columns type accordingly? With that I think this PR could be merged in the upcoming v6. Thank you upfront.

[Chienlin1014]

@fmbenhassine Thank you for the quick review and the clear guidance!
I've just added the migration script for v6.0 under src/main/resources/org/springframework/batch/core/migration/6.0/migration-sqlserver.sql, following the same structure and comments style as the v5.0 script.
It includes the corresponding ALTER TABLE statements to update the affected columns to NVARCHAR types.

Please let me know if you'd like me to adjust anything.
Thank you again for the review and for considering this PR for inclusion in v6.0!