Update default configuration handling and integrate NyxResult into config.rs

- Introduced `DEFAULT_CONFIG_TOML` to simplify default configuration loading.
- Replaced `show_progress` with `quiet` in configuration for improved clarity.
- Refactored `create_example_config` to use `NyxResult` and streamline logic with fallback handling.
- Added `default-nyx.conf` file for default configuration management.
- Enhanced `merge_configs` to include new parameters like `scan_timeout_secs` and `quiet`.

src/errors.rs

@@ -10,6 +10,9 @@ pub enum NyxError {
     #[error("I/O error: {0}")]
     Io(#[from] std::io::Error),
 
+    #[error("TOML parse error: {0}")]
+    Toml(#[from] toml::de::Error),
+
     #[error("SQLite error: {0}")]
     Sql(#[from] rusqlite::Error),