Add error handling with NyxError and refactor console output formatting

- Introduced `NyxError` and `NyxResult` for unified error handling across modules.
- Refactored `scan.rs`, `index.rs`, and `walk.rs` with improved error management and consistent formatting.
- Replaced existing error handling in `database.rs` with `NyxResult`.
- Improved database maintenance by integrating `vacuum` and `clear` methods into workflows.
- Added `dashmap` for efficient parallel diagnostics result aggregation in `scan_with_index_parallel`.
- Enhanced readability and formatting of console outputs in multiple modules.

src/utils/ext.rs

@@ -0,0 +1,15 @@
+pub fn lowercase_ext(path: &std::path::Path) -> Option<&'static str> {
+  path.extension()
+    .and_then(|s| match s.to_str()? {
+      "rs"  | "RS"  => Some("rs"),
+      "c"           => Some("c"),
+      "cpp" | "c++" => Some("cpp"),
+      "java"        => Some("java"),
+      "go"          => Some("go"),
+      "php"         => Some("php"),
+      "py"  | "PY"  => Some("py"),
+      "ts" | "TSX"  | "tsx" => Some("ts"),
+      "js"          => Some("js"),
+      _ => None,
+    })
+}