Enhance syncback functionality with sourcemap generation

- Introduced a new function `write_sourcemap_from_syncback` to generate sourcemaps directly from in-memory data, improving performance by eliminating the need for file reads during sourcemap creation.
- Updated the `syncback_loop` to return a `SyncbackResult` struct, encapsulating filesystem operations and instance paths for better post-processing.
- Modified the `SyncbackCommand` to utilize the new sourcemap generation method, allowing for parallel execution of file writes and sourcemap creation.

These changes streamline the syncback process and enhance the efficiency of sourcemap generation.

src/lib.rs

@@ -36,5 +36,5 @@ pub use snapshot::{
     RojoDescendants, RojoTree,
 };
 pub use snapshot_middleware::{snapshot_from_vfs, Middleware, ScriptType};
-pub use syncback::{syncback_loop, FsSnapshot, SyncbackData, SyncbackSnapshot};
+pub use syncback::{syncback_loop, FsSnapshot, SyncbackData, SyncbackResult, SyncbackSnapshot};
 pub use web::interface as web_api;