fix(plugin-mssql): use active schema for object queries

[andiahmads]

Summary

• Resolve MSSQL object queries against the active schema when callers do not pass an explicit schema.
• Keep explicit schema arguments taking precedence over the active schema.
• Add TableProMSSQLCore tests for schema resolution and non-dbo browse query generation.

Root cause

MSSQL browse, filter, and generated edit statements treated a nil schema as unqualified object access. For connections whose active schema was not dbo, this produced queries like SELECT * FROM [Orders], which SQL Server resolved through the login default schema instead of the selected schema.

Fixes #1774

Validation

• swift test --package-path Packages/TableProCore --filter MSSQLSchemaQueriesTests
• xcodebuild -project TablePro.xcodeproj -scheme TablePro -configuration Debug -skipPackagePluginValidation CODE_SIGNING_ALLOWED=NO build
• git diff --check
• swiftlint lint --strict