fix: reorder AST folding after semantics validation

[tserg]

What I did

Fix #2830, and stricter type safety for literal operations.

How I did it

• Reorder AST folding to after semantics validation.
• Added not_assignable flag to BaseTypeDefinition.
• Added annotation of constants, and helper functions to derive foldable values where required for semantics validation before AST nodes are folded.

How to verify it

See new tests, and updated tests.

Commit message

fix: reorder AST folding after semantics validation

Fixes an issue with type-checking and bounds-check of literal ops.

With the reordering, a `not_assignable` flag has been added to 
`BaseTypeDefinition`, aligning with the intent behind `check_kwargable`.
This allows true constants (builtin or user-defined) to be differentiated
from calldata arguments which are not assignable, but not constants.

Helper functions have also been added to support the derivation of foldable
values for semantics validation and to determine whether a node is foldable
 prior to their AST folding.

Fix #2830

Description for the changelog

Type-check and bounds-check literal ops involving literals from constant folding.

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #2832 (2001f11) into master (f31f0ec) will decrease coverage by 0.18%.
The diff coverage is 83.09%.

@@            Coverage Diff             @@
##           master    #2832      +/-   ##
==========================================
- Coverage   88.29%   88.11%   -0.19%     
==========================================
  Files          97       97              
  Lines       10919    10988      +69     
  Branches     2583     2558      -25     
==========================================
+ Hits         9641     9682      +41     
- Misses        830      864      +34     
+ Partials      448      442       -6     

Impacted Files	Coverage Δ
vyper/semantics/types/function.py	87.12% <ø> (ø)
vyper/semantics/types/indexable/mapping.py	96.42% <ø> (ø)
vyper/semantics/types/value/address.py	100.00% <ø> (ø)
vyper/semantics/types/indexable/sequence.py	87.23% <50.00%> (-0.71%)	⬇️
vyper/builtin_functions/functions.py	90.68% <69.82%> (+0.28%)	⬆️
vyper/semantics/validation/annotation.py	91.25% <70.00%> (+1.58%)	⬆️
vyper/semantics/types/utils.py	88.35% <82.60%> (-1.41%)	⬇️
vyper/semantics/validation/local.py	91.34% <83.33%> (+0.13%)	⬆️
vyper/semantics/validation/utils.py	90.00% <88.23%> (-1.35%)	⬇️
vyper/ast/folding.py	87.90% <100.00%> (-4.72%)	⬇️
... and 18 more

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[charles-cooper]

looks like there is some code that is duplicated in structure. is there some way we can refactor _validate_numeric_bounds to address these cases?

[charles-cooper]

it is also very weird to see typechecking code in AST construction. is it possible to move these to the constant folder module?

[tserg]

looks like there is some code that is duplicated in structure. is there some way we can refactor _validate_numeric_bounds to address these cases?

I have moved the typechecking to folding.py so it only runs after _validate_numeric_bounds for BinOp and Compare nodes.