[Caideyipi]

Description

Recent master CI logs show IoTDBAlterTimeSeriesTypeIT.testWriteAndAlter taking 213 seconds and IoTDBSessionSchemaTemplateIT taking 217 seconds in Cluster IT - 1C3D. The table-model testWriteAndAlter takes 85 seconds in Table Cluster IT - 1C3D.

• Batch the schema type-conversion fixtures into 512/520-row tablets at the existing flush and type-change boundaries. Keep the same rows, conversion pairs, aligned/unaligned and sequence/unsequence cases, and query assertions.
• Start the Session schema-template cluster once per schema-engine parameter, reducing cluster initializations from 14 to 2. Close the Session and clear databases, templates and users after each method.
• Check Pipe and subscription eventual assertions immediately, retaining the one-second retry interval, existing timeouts and continuous observation windows.
• Replace the five-second sleeps after synchronous DataNode shutdown in tree/table Pipe failover tests with process-exit assertions.

Validation

• mvn -o -pl integration-test -P with-integration-tests spotless:apply passed.
• mvn -o -pl integration-test -P with-integration-tests test-compile -DskipTests passed, including Checkstyle and Spotless checks.
• Tree-model IoTDBAlterTimeSeriesTypeIT#testWriteAndAlter and all 14 IoTDBSessionSchemaTemplateIT tests passed locally (Memory and PBTree). The Session template class completed in 28.9 seconds on the local Windows 1C1D environment; the CI observations above use different runners/topologies.
• Table-model IoTDBAlterColumnTypeIT#testWriteAndAlter passed locally.
• Attempted the four tree/table IoTDBPipeClusterIT#testMachineDowntimeAsync+testMachineDowntimeSync cases. The local Windows machine exhausted its commit memory during JVM startup, so this run could not complete; these cases still need CI validation.
• Subscription IT sources compile; the Apache POM excludes the subscription IT suite from regular execution.

This PR has:

• been self-reviewed.
• modified existing integration tests.