[Test] Avoid metadata lease fencing in DataNode unit tests

[Caideyipi]

Description

DataNode unit-test JVMs do not receive ConfigNode heartbeats. When a cache-related test class runs for more than the 20-second metadata lease threshold, the singleton MetadataLeaseManager fences the local caches and causes unrelated test failures such as TreeViewTest.

Configure the DataNode unit-test environment to disable the background metadata lease check. This only changes src/test/resources; production and integration-test configurations are unaffected. The metadata lease tests keep their coverage because they use independently constructed managers with injected clocks.

Setting the test-wide check interval avoids duplicating lease recovery setup across every cache test and also protects future unit tests that use the same guarded singletons.

Verification

• git diff --check
• DataNode unit tests on Ubuntu: passed
• DataNode unit tests on Windows: passed

This PR has:

• been self-reviewed.
• added a comment explaining why metadata lease checking is disabled for unit tests.
• updated the shared unit-test configuration to cover existing cache tests.

Key changed/added classes (or packages if there are too many classes) in this PR

• iotdb-core/datanode/src/test/resources/iotdb-system.properties