Clean up log level usage

[mrfelton]

This pull request includes several changes to the logging statements across multiple files to standardize the log message format. The primary change involves replacing the msg key with message in the log objects.

Standardization of log message format:

• src/lib/DataProviderManager.ts: Updated log statements to use message instead of msg for consistency. [1] [2] [3] [4] [5]
• src/lib/util.ts: Changed the log level from error to warn and updated the log message format.
• src/providers/bitcoind.ts: Standardized log messages by replacing msg with message. [1] [2] [3] [4]
• src/providers/esplora.ts: Updated error log message format to use message instead of msg.
• src/providers/mempool.ts: Updated error log message format to use message instead of msg.
• src/server.tsx: Standardized log messages by replacing msg with message. [1] [2]