[317787106]

What does this PR do?

Fixes three shared test-fixture issues:

• AccountIdIndexStoreTest: replace random account-ID bytes with five distinct ASCII IDs that remain distinct after UTF-8 decoding and lowercase normalization.
• RelayServiceTest.testStrictHelloAuthentication: populate the genesis, solid and head block hashes so the HELLO fixture passes structural validation and reaches the authentication assertions.
• TransactionsMsgHandlerTest: inject a mocked FetchBlockService into the standalone AdvService used by the disconnect-recovery fixture, including testInvalidSignatureDisconnectWaitsForBusyAnnouncer.

Why are these changes required?

Avoid random account-ID key collisions and complete the fixtures needed for authentication and disconnect-recovery tests.

This PR has been tested by:

All 40 tests across the three classes passed on ARM64 / JDK 17. CI-scoped Checkstyle and git diff --check passed.

Follow up

None.

Extra details

Test fixtures only.