fix(gen): correct two latent lookup bugs exposed by the new call order

- ExprGenOps called `_lookup_module_sha1` on ExprGenAttr, but the method
  lives on CallGenBase. With ExprGenOps now translated before the
  callee's stub/text.ll is available, the receiver lookup failed with
  "method return type cannot be obtained precisely":
  `cls=ExprGenAttr ... _lookup_module_sha1`. Use
  `self.Gen.CallGenBase._lookup_module_sha1`.
- VpiReader._lookup_vpi_ret_annot's generic-specialization fallback used
  `sha1_len` without declaring it. The new `list[int].set` return-type
  lookup reaches that fallback and failed with
  `NameError: undefined name 'sha1_len'`. Compute
  `sha1_len = strlen(src_sha1)` before the cache scan.

Self-host 110/110 (two generations); ListTest, GenericTest3, PtrOpProbe
and HashLibTest pass.

App/lib/Stub/StubGen/VpiReader.vp

@@ -1741,6 +1741,7 @@ def _lookup_vpi_ret_annot(src_sha1: str, cls_name: str, method_name: str) -> str
     """Look up a method's cached return-annotation string; None if not found."""
     if _g_vpi_ret_keys is None or _g_vpi_ret_count == 0: return None
     if src_sha1 is None or method_name is None: return None
+    sha1_len: sizet = string.strlen(src_sha1)
     key_buf: bytes = _vpi_method_key(src_sha1, cls_name, method_name)
     if key_buf is None: return None
     i: int

App/lib/core/Gen/Expr/ExprGenOps.vp

@@ -400,7 +400,7 @@ novirtual class ExprGenOps(ExprGenBase.ExprGenBase):
                         mod_path = om_buf_mg
         # package submodules (`intr.idt`) count as known when the package is imported
         if self.Gen.ImportsGen.is_module_imported_or_known(trans._imported_modules, mod_path) == 0: return None
-        gv: mlirlite.GlobalVariable* = self.Gen.ExprGenAttr.find_global_in_module(trans.Module, self.Gen.FuncGenBase._mangle_name_with_sha1(self.Gen.ExprGenAttr._lookup_module_sha1(mod_path), at.attr))
+        gv: mlirlite.GlobalVariable* = self.Gen.ExprGenAttr.find_global_in_module(trans.Module, self.Gen.FuncGenBase._mangle_name_with_sha1(self.Gen.CallGenBase._lookup_module_sha1(mod_path), at.attr))
         if gv is None: gv = self.Gen.ExprGenAttr.find_global_in_module(trans.Module, at.attr)
         if gv is None or gv.Ty is None: return None
         # a global is usually `Element*` / `Element**` or an array `[N]Element`: descend to the leaf type