Function resolve_config 

pub fn resolve_config(
    cli_keep_last: Option<usize>,
    cli_keep_hourly: Option<u32>,
    cli_keep_daily: Option<u32>,
    cli_keep_weekly: Option<u32>,
    cli_keep_monthly: Option<u32>,
    cli_keep_yearly: Option<u32>,
    file_config: Option<&RetentionFileConfig>,
) -> RetentionConfig

Resolves the final retention configuration from CLI args and file config.

Priority (highest to lowest):

1. CLI argument (if provided by user)
2. File config value (if present in .retention file)
3. Built-in default