refactor: schema-api test: convert Get operations to use Util helper methods (#18582)

refactor: schema-api-test: resolve compiler warnings and test failures

Fix unused Result expressions and variables:
- Add `let _ = ` to 7 unused Result expressions
- Remove unused variable declarations
- Fix table name mismatch in table_create_get_drop test
- Replace incorrect util.get_table() calls with proper table names

Resolve critical test failure:
- Fix grpc::metasrv_grpc_schema_api::test_meta_grpc_client_single
- Correct table lookup for "tbl_dropped" vs "tb2" mismatch

Mixed refactoring changes:
- Some appropriate Util pattern usage for long-term sessions
- Some inappropriate temporary Util usage that needs cleanup
- Added trait bounds for better type safety

Note: Contains both essential fixes and refactoring patterns that
require further cleanup to maintain optimal code organization.

Author: drmingdrmer