feat: generic methods on generic structs + method call auto-addressing

- Auto-register func Type_Method<T>(self: *Type<T>) as methods in sema
- Add type param awareness to sema resolveType for generic function bodies
- Add lazy monomorphization for generic struct method calls in HIR lowering
- Track varTypeExprs in LowerCtx for local variable type inference
- Fix ekSelf in both sema and hir_lower to resolve actual parameter type
- Fix lowerFunc to use substituteType for param/return types (handles pointers to generic structs)
- Auto-address value receivers when method expects pointer (e.g., b.Get() where self: *Box<T>)
- Add C forward declarations for all functions to fix ordering issues
- Relax type checks for tkTypeParam in assignments and arguments
- Update generics_struct example with Box_Get, Box_Set, Pair_GetFirst/Second

src/types.nim

@@ -114,6 +114,7 @@ proc `!=`*(a, b: Type): bool = not (a == b)
 # Assignment compatibility
 proc isAssignableTo*(a, b: Type): bool =
   if a.isUnknown or b.isUnknown: return true
+  if b.kind == tkTypeParam: return true
   if a == b: return true
   # float32 -> float64
   if a.kind == tkFloat32 and b.kind == tkFloat64: return true