Add support for detecting tests in source files, and implement it for Rust (#11195)

Continuing work from #10873 

Release Notes:

- N/A

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Co-authored-by: Mikayla <mikayla@zed.dev>

crates/workspace/src/workspace.rs

@@ -8,6 +8,7 @@ mod persistence;
 pub mod searchable;
 pub mod shared_screen;
 mod status_bar;
+pub mod tasks;
 mod toolbar;
 mod workspace_settings;