Fix #66, #31 and #72

[demarco2016]

Hey Arc team,

I picked up and resolved 3 open issues from the tracker:

#66 - Move RemoteSigningConfig and RetryConfig to unit tests

• Moved config_builder_pattern and retry_config_validation tests from client.rs to the unit test section in config.rs
• Converted tests from #[tokio::test] to standard #[test] since async was unnecessary

#31 - WSL2: latency_setup.sh fails due to missing tc module

• Added WSL2 detection at the top of the generated latency_setup.sh script
• Script now exits gracefully with a clear message instead of failing on tc commands when running under WSL2

#72 - Implement caching for ConsensusBlock size

• Replaced the TODO in size_bytes() with actual caching using OnceLock<ByteSize>
• Added cached_size_bytes field to ConsensusBlock with lazy initialization on first access
• Updated all related struct constructions across 10 files
• Manually implemented Clone to support the OnceLock field properly