chore(tests): replace pubsubTopic references with shardInfo + clusterId

[danisharora099]

Description

The nwaku node is deprecating the usage of pubsubTopic in favor of using shardInfo + clusterId. While the initial PR (#2239) updated the CI configuration, we need to update our test suite to align with this change.
Currently, our test suite in the packages/tests directory still contains many references to pubsubTopic when interacting with nwaku/service node. These should be converted to use shardInfo types to match nwaku's new approach.

User Story

As a Waku developer, I want to update our test suite to use shardInfo + clusterId instead of pubsubTopic when interacting with nwaku, so that:

• Our tests reflect the current best practices for nwaku configuration
• We maintain consistency with nwaku's deprecation of pubsubTopic

Proposed Solution / Feature Design

1. Audit and update test files in packages/tests to:

• Replace direct pubsubTopic usage with appropriate shardInfo + clusterId combinations
• Update test utilities and helpers to use sharding-based APIs
• Maintain compatibility with nwaku's REST API which still uses pubsubTopic in endpoints

2. Key files to update:

• packages/tests/src/lib/service_node.ts: Update interface while maintaining REST API compatibility
• Test files under packages/tests/tests/ that use pubsubTopic directly
• Test utilities and helpers that generate test data with pubsubTopic
• Ensure all tests continue to pass with the updated approach