Extensions: Add cache decorators as appropriate

I noticed that many plugins were creating duplicate per-process
translation layers - for instance, `windows.envars.Envars` was ending up
with > 30 process layers per process due to repeated calls to
`get_peb()`, which calls `add_process_space()` internally.

This adds `@functools.lru_cache` to the `get_peb()` and `get_peb32()`
methods on the `EPROCESS` extension, since these should only need to be
created once.

Also adds `@functools.lru_cache` to `add_process_space` to enable
reusing the same process address space, provided the same arguments are
passed to the `add_process_space()` method.

volatility3/framework/symbols/linux/extensions/__init__.py

@@ -471,6 +471,7 @@ class task_struct(generic.GenericIntelProcess):
 
         return True
 
+    @functools.lru_cache
     def add_process_layer(
         self, config_prefix: Optional[str] = None, preferred_name: Optional[str] = None
     ) -> Optional[str]:

volatility3/framework/symbols/mac/extensions/__init__.py

@@ -2,6 +2,7 @@
 # which is available at https://www.volatilityfoundation.org/license/vsl-v1.0
 #
 import contextlib
+import functools
 import logging
 from typing import Generator, Iterable, Optional, Set, Tuple
 
@@ -17,6 +18,7 @@ class proc(generic.GenericIntelProcess):
     def get_task(self):
         return self.task.dereference().cast("task")
 
+    @functools.lru_cache
     def add_process_layer(
         self, config_prefix: Optional[str] = None, preferred_name: Optional[str] = None
     ) -> Optional[str]:

volatility3/framework/symbols/windows/extensions/__init__.py

@@ -732,9 +732,10 @@ class EPROCESS(generic.GenericIntelProcess, pool.ExecutiveObject):
 
         return True
 
+    @functools.lru_cache
     def add_process_layer(
         self, config_prefix: Optional[str] = None, preferred_name: Optional[str] = None
-    ):
+    ) -> str:
         """Constructs a new layer based on the process's DirectoryTableBase."""
 
         parent_layer = self._context.layers[self.vol.layer_name]
@@ -761,6 +762,7 @@ class EPROCESS(generic.GenericIntelProcess, pool.ExecutiveObject):
             self._context, dtb, config_prefix, preferred_name
         )
 
+    @functools.lru_cache
     def get_peb(self) -> interfaces.objects.ObjectInterface:
         """Constructs a PEB object"""
         if constants.BANG not in self.vol.type_name:
@@ -786,6 +788,7 @@ class EPROCESS(generic.GenericIntelProcess, pool.ExecutiveObject):
         )
         return peb
 
+    @functools.lru_cache
     def get_peb32(self) -> Optional[interfaces.objects.ObjectInterface]:
         """Constructs a PEB32 object"""
         if constants.BANG not in self.vol.type_name: