Summary

• Fix flaky BaseNetTest by adding null guards in destroy() and using random port for P2P listener to avoid port conflicts
• Move test-only constant TEST_CONF from production Constant.java to new TestConstants.java in the test module
• Rename TESTNET_CONF to NET_CONF for clarity since config.conf serves all network types

Changes

• common/src/main/java/org/tron/core/Constant.java: Remove TEST_CONF, rename TESTNET_CONF → NET_CONF
• framework/src/test/java/org/tron/common/TestConstants.java: New test constants class
• framework/src/test/java/org/tron/core/net/BaseNet.java: Add null guards in destroy(), use random port
• 207 test files: Update Constant.TEST_CONF → TestConstants.TEST_CONF
• 4 production files: Update Constant.TESTNET_CONF → Constant.NET_CONF

Test plan

• Full test suite: 2271 tests passed (1 retried, 24 skipped), BUILD SUCCESSFUL
• Representative tests verified: ArgsTest, ManagerTest, TransferActuatorTest, P2pEventHandlerImplTest, GlobalRateLimiterTest, SolidityNodeTest