test: migrate unit tests from JUnit 4 to JUnit 5 in code-generator, configcenter and limiter modules

[drow931]

What type of PR is this?

• Bug fix
• New feature
• Code refactoring
• Test improvement
• Documentation update
• CI/CD improvement

What this PR does / why we need it

This PR migrates unit tests from JUnit 4 to JUnit 5 (Jupiter) across three modules to ensure compatibility with Spring Boot 3.x and align with modern testing practices.

Which modules are affected

• trpc-code-generator
• trpc-configcenter/trpc-configcenter-nacos
• trpc-configcenter/trpc-configcenter-open-polaris
• trpc-limiter/trpc-limiter-sentinel

Changes

API Migration

JUnit 4	JUnit 5
org.junit.Assert	org.junit.jupiter.api.Assertions
org.junit.Test	org.junit.jupiter.api.Test
org.junit.BeforeClass	org.junit.jupiter.api.BeforeAll
Assert.assertEquals()	Assertions.assertEquals()
Assert.assertTrue()	Assertions.assertTrue()
Assert.assertFalse()	Assertions.assertFalse()
Assert.assertNotNull()	Assertions.assertNotNull()

Files Changed (25 files)

• trpc-code-generator: 6 test files migrated
• trpc-configcenter-nacos: 1 test file migrated + pom.xml updated
• trpc-configcenter-open-polaris: 2 test files migrated + pom.xml updated
• trpc-limiter-sentinel: 14 test files migrated + pom.xml updated

Special notes for your reviewer

1. No functional changes - this is a pure test framework migration
2. All existing test logic and assertions remain unchanged
3. JUnit 5 dependencies have been added to the relevant pom.xml files where needed
4. This change is part of the ongoing effort to modernize the test infrastructure for Spring Boot 3.x compatibility

Does this PR introduce a breaking change?

• No

How Has This Been Tested?

• All migrated unit tests pass successfully
• Verified no regression in test coverage

Checklist

• I have read the CONTRIBUTING document
• My code follows the code style of this project
• I have added/updated tests to cover my changes
• All new and existing tests passed