feat: add suitelink client runtime and test harness

tests/SuiteLink.Client.IntegrationTests/README.md

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+# SuiteLink Integration Tests
+
+These tests are intentionally safe by default and run only when explicitly enabled.
+
+## Enable
+
+Set:
+
+- `SUITELINK_IT_ENABLED=true`
+
+Required connection variables:
+
+- `SUITELINK_IT_HOST`
+- `SUITELINK_IT_APPLICATION`
+- `SUITELINK_IT_TOPIC`
+- `SUITELINK_IT_CLIENT_NAME`
+- `SUITELINK_IT_CLIENT_NODE`
+- `SUITELINK_IT_USER_NAME`
+- `SUITELINK_IT_SERVER_NODE`
+
+Optional connection variables:
+
+- `SUITELINK_IT_PORT` (default `5413`)
+- `SUITELINK_IT_TIMEZONE` (defaults to `UTC` via `SuiteLinkConnectionOptions`)
+
+Optional tag variables (tests run only for the tags provided):
+
+- `SUITELINK_IT_BOOL_TAG`
+- `SUITELINK_IT_INT_TAG`
+- `SUITELINK_IT_FLOAT_TAG`
+- `SUITELINK_IT_STRING_TAG`
+
+## Notes
+
+- If integration settings are missing, tests return immediately and do not perform network calls.
+- These tests are intended as a live harness, not deterministic CI tests.