Loop Transformations: Cutting and Peeling

This MR introduces a number of loop transformations and their prequesites to the new backend.

• Add CanonicalClone pass: Clone an AST and duplicate all symbols declared inside it to retain canonicality
• Add ReshapeLoops pass collection:
  • cut_loop reimplements loop cutting like available through the old pystencils.transformations.cut_loop
  • peel_loop_front implements loop peeling, often the better alternative to cut_loop

Changes on the side:

• Move canonical duplication of symbols to the KernelCreationContext
• Add documentation for the transformations module
• Extend documentation of KernelCreationContext
• Improved AstFactory interface: introduce parse_index and clarify type hints

To Do:

• Test cases for loop cutting
• Test cases for loop peeling

src/pystencils/backend/transformations/eliminate_constants.py

-from typing import cast, Iterable
+from typing import cast, Iterable, overload
 from collections import defaultdict
 
 from ..kernelcreation import KernelCreationContext, Typifier
@@ -116,6 +116,14 @@ class EliminateConstants:
         self._fold_floats = False
         self._extract_constant_exprs = extract_constant_exprs
 
+    @overload
+    def __call__(self, node: PsExpression) -> PsExpression:
+        pass
+
+    @overload
+    def __call__(self, node: PsAstNode) -> PsAstNode:
+        pass
+
     def __call__(self, node: PsAstNode) -> PsAstNode:
         ecc = ECContext(self._ctx)