Make cores_per_node and mem_per_node regular provider attributes (#3988)

Prior to this PR, these were defined with @Property which passed through
directly to underlying state attributes.

Moving from mypy 1.5.1 to 1.18.2 in testing revealed that the type
annotations on the property setters were incorrect. For example,

```
parsl/providers/slurm/slurm.py:174: error: Incompatible types in assignment
(expression has type "int | None", variable has type "int")  [assignment]
```

As part of tidying that up, it seemed to me that those property methods
weren't necessary at all.

This PR removes property behaviour for those attributes. The type
annotations are now defined in ExecutionProvider.__init__ (unchanged as
already correct). The documentation which used to live on the @Property
is moved to the class level docstring.

## Type of change

- Code maintenance/cleanup

Author: benclifford

parsl/providers/base.py

@@ -33,7 +33,28 @@ class ExecutionProvider(metaclass=ABCMeta):
           [cancel]     <--------|----+
                                 |
                                 +-------------------
-     """
+
+    In addition to the listed methods, an ExecutionProvider instance must always
+    have these attributes, which both default to `None`:
+
+      mem_per_node: Real memory to provision per node in GB.
+
+                    Providers which set this attribute should ask for mem_per_node of memory
+                    when provisioning resources, and set the corresponding environment
+                    variable PARSL_MEMORY_GB before executing submitted commands.
+
+                    If this attribute is set, executors may use it to calculate how many tasks can
+                    run concurrently per node.
+
+      cores_per_node: Number of cores to provision per node.
+
+                    Providers which set this attribute should ask for cores_per_node cores
+                    when provisioning resources, and set the corresponding environment
+                    variable PARSL_CORES before executing submitted commands.
+
+                    If this attribute is set, executors may use it to calculate how many tasks can
+                    run concurrently per node.
+    """
 
     @abstractmethod
     def __init__(self) -> None:
@@ -44,8 +65,8 @@ def __init__(self) -> None:
         self.script_dir: Optional[str]
         self.parallelism: float
         self.resources: Dict[object, Any]
-        self._cores_per_node: Optional[int] = None
-        self._mem_per_node: Optional[float] = None
+        self.cores_per_node: Optional[int] = None
+        self.mem_per_node: Optional[float] = None
         pass
 
     @abstractmethod
@@ -111,40 +132,6 @@ def label(self) -> str:
         ''' Provides the label for this provider '''
         pass
 
-    @property
-    def mem_per_node(self) -> Optional[float]:
-        """Real memory to provision per node in GB.
-
-        Providers which set this property should ask for mem_per_node of memory
-        when provisioning resources, and set the corresponding environment
-        variable PARSL_MEMORY_GB before executing submitted commands.
-
-        If this property is set, executors may use it to calculate how many tasks can
-        run concurrently per node.
-        """
-        return self._mem_per_node
-
-    @mem_per_node.setter
-    def mem_per_node(self, value: float) -> None:
-        self._mem_per_node = value
-
-    @property
-    def cores_per_node(self) -> Optional[int]:
-        """Number of cores to provision per node.
-
-        Providers which set this property should ask for cores_per_node cores
-        when provisioning resources, and set the corresponding environment
-        variable PARSL_CORES before executing submitted commands.
-
-        If this property is set, executors may use it to calculate how many tasks can
-        run concurrently per node.
-        """
-        return self._cores_per_node
-
-    @cores_per_node.setter
-    def cores_per_node(self, value: int) -> None:
-        self._cores_per_node = value
-
     @property
     @abstractmethod
     def status_polling_interval(self) -> int: