python: Add task for running modules (#26462)

Closes #26460

I am new to contributing to Zed (and pretty new to Rust in general). I'm
not too familiar with code style, guidelines etc. so please feel free to
suggest changes/improvements.

This PR adds a run icon to Python files that have a "main" function:
```python
if __name__ == "__main__":
    ...
```

In addition to the gutter icon, there is now also an extra task in the
command palette "run module".

Release Notes:

- Added detection for runnable Python modules
- Added Python-specific task to run a Python file as a module from
inside the project's scope

---------

Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>

crates/languages/src/python/runnables.scm

@@ -82,3 +82,19 @@
         )
     )
 )
+
+; module main method
+(
+    (module
+        (if_statement
+            condition: (comparison_operator
+                (identifier) @run @_lhs
+                operators: "=="
+                (string) @_rhs
+            )
+            (#eq? @_lhs "__name__")
+            (#match? @_rhs "^[\"']__main__[\"']$")
+            (#set! tag python-module-main-method)
+        )
+    )
+)