Remove DATAFUSION_RAY_LOG_LEVEL and Migrate to RUST_LOG

[NGA-TRAN]

The DATAFUSION_RAY_LOG_LEVEL environment variable was carried over from the original Python-based project and is no longer relevant.

To simplify and standardize logging, we should:

• Remove all references to DATAFUSION_RAY_LOG_LEVEL
• Migrate logging configuration to rely exclusively on the standard RUST_LOG environment variable
• Ensure log levels are consistently respected across binaries and components

This will align the project with common Rust practices and avoid confusion from legacy settings.

[NGA-TRAN]

Done in #42 and/or #43