test: cover DM data types and connection options

[skhe]

Summary

• Add 38 real-DM P1 cases for scalar and NULL round trips, connection address forms, cursor shape, schema, autocommit, isolation, and common option parsing.
• Fix TIME binding shifting five minutes under Asia/Shanghai historical timezone rules. Run the hosted real-DM suite with TZ=Asia/Shanghai to retain the regression signal.
• Record the observed type mapping, tested limits, and the remaining high-precision DECIMAL(30,8) write defect.

Verification

• Official DM8 ARM64 on local OrbStack: 104 passed, 0 failed/errors/skipped on each of CPython 3.9–3.13.
• go test ./..., actionlint, workflow YAML and version checks passed locally.

Known gap

Binding 12345678901234567890.12345678 to DECIMAL(30,8) stores a zero fractional part. This PR documents the failure; it is not safe to claim that high-precision decimal writes are covered. Timeout and app-name effectiveness also need dedicated checks.