Log improvements 4.0.3

[SurfingNerd]

This pull request introduces several updates related to chain spec handling, logging improvements, and dependency management. The most significant changes are the addition of new chain spec functions for Diamond and Diamond Testnet, a switch to a forked bn dependency, and some minor logging and versioning tweaks.

Chain spec enhancements:

• Added new functions new_diamond and new_diamond_testnet to crates/ethcore/src/ethereum/mod.rs for loading Diamond and Diamond Testnet chain specs, and renamed the mainnet function to new_ethereum for clarity. defaulting to Diamond chain spec #337

Dependency updates:

• Updated the bn dependency in crates/vm/builtin/Cargo.toml to use the substrate-bn fork from the dmdcoin GitHub repository instead of the original Parity version.

Logging improvements:

• Changed a consensus error log in crates/ethcore/sync/src/api.rs from info! to debug! level to reduce log verbosity for non-critical errors.
• Improved block import failure warning in crates/ethcore/src/client/client.rs to include both the best block number and hash for better debugging context.

Versioning:

• Bumped crate version in Cargo.toml from 4.0.2 to 4.0.3-rc1.