Add BDD test suite covering V2 SDK functionality

[b3y0urs3lf]

Ports the TypeScript SDK's BDD coverage to Java, mirroring scenarios across aggregator communication, token minting/transfer/verification, splits, payments, sharding, CBOR envelope strictness, and inclusion proofs. Covers the V2 PR chain (#53, #54, #59, #61, #62, #63, #65) end-to-end against both the hermetic in-process aggregator and the real BFT-shard topology via subscription proxy.

• 49 Cucumber feature files (~149 scenario declarations)
• 33 step-definition classes wired through PicoContainer
• Test-only support clients: StrictTestAggregatorClient, ForgivingTestAggregatorClient, ShardAwareAggregatorClient, SimulatedShardPool, NametagRegistry, TokenTree(Builder)
• Tag-based runtime gating: @hermetic-only, @bft-shard-only, @multi-shard-only, @pending-src-cleanup, @stateful, @fresh-aggregator, @slow
• Env wiring: AGGREGATOR_URL, AGGREGATOR_API_KEY, TRUST_BASE_PATH
• JUnit Platform Suite runner with package selection

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive Cucumber-based end-to-end testing suite for the Unicity SDK, including new test tasks in build.gradle.kts, a robust test context management system, and numerous step definitions covering token lifecycle, addressing, serialization, and security scenarios. The reviewer provided actionable feedback regarding the Gradle configuration to avoid overwriting system properties and suggested safer shutdown patterns for the ExecutorService in the shard load tests.

[gemini-code-assist]

Assigning to systemProperties replaces the entire map of system properties for the test task. This causes the cucumber.junit-platform.naming-strategy property set on the previous line to be lost unless it is also present in the host JVM's system properties. Use the systemProperties() method instead to append properties to the existing map. This pattern is repeated in several other BDD tasks (bddNametag, bddSlow, etc.).

    systemProperty("cucumber.junit-platform.naming-strategy", "long")
    systemProperties(System.getProperties().toMap() as Map<String, Any>)

[gemini-code-assist]

The ExecutorService is shut down using shutdown(), which allows existing tasks to continue running. In a test environment, especially if a timeout occurs (line 166), it is safer to use shutdownNow() to attempt to stop active tasks and prevent resource leaks or interference with subsequent tests. Additionally, calling awaitTermination ensures the pool is fully cleaned up before the method returns.

        exec.shutdownNow();
        exec.awaitTermination(5, TimeUnit.SECONDS);