Add missing escape hatch tests

[adamiak]

Resolves L2B-1934

[linear]

L2B-1934 Add missing unit tests

To accelerate merge of PR #421 a few modifications miss unit test. It is essential to add these unit tests before project is finalaised. Here's a list of files that have new functionality not covered by unit tests. Add them:

• packages/backend/src/peripherals/database/StateUpdateRepository.ts
• packages/backend/src/core/FreezeCheckService.ts
• packages/backend/src/api/controllers/UserController.ts
• packages/backend/src/api/controllers/getEscapableAssets.ts
• packages/backend/src/api/controllers/serializeMerkleProofForEscape.ts
• packages/state/src/MerkleTree.ts
• packages/state/src/PositionLeaf.ts
• packages/backend/src/peripherals/ethereum/EthereumClient.ts
• packages/encoding/src/encoding/encodeState.ts