Delete evaluator.py shim: all imports go directly to bootstrapped sx_ref.py

EvalError moved to types.py. All 27 files updated to import eval_expr,
trampoline, call_lambda, etc. directly from shared.sx.ref.sx_ref instead
of through the evaluator.py indirection layer. 320/320 spec tests pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/platform_py.py

@@ -600,7 +600,7 @@ def sx_expr_source(x):
 
 
 try:
-    from shared.sx.evaluator import EvalError
+    from shared.sx.types import EvalError
 except ImportError:
     class EvalError(Exception):
         pass