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/errors.rs

@@ -0,0 +1,24 @@
+use thiserror::Error;
+
+pub type NyxResult<T, E = NyxError> = core::result::Result<T, E>;
+
+#[derive(Debug, Error)]
+pub enum NyxError {
+  #[error("I/O error: {0}")]
+  Io(#[from] std::io::Error),
+
+  #[error("SQLite error: {0}")]
+  Sql(#[from] rusqlite::Error),
+
+  #[error("tree-sitter error: {0}")]
+  TreeSitter(#[from] tree_sitter::LanguageError),
+
+  #[error("connection-pool error: {0}")]
+  Pool(#[from] r2d2::Error),
+
+  #[error("time error: {0}")]
+  Time(#[from] std::time::SystemTimeError),
+
+  #[error("other: {0}")]
+  Other(String),
+}