Document known typecheck failures.

conservancy_beancount/data.py

@@ -95,7 +95,7 @@ class Posting(BasePosting):
     # of Beancount's type declaration being a smidge too specific: I think it
     # would be very unusual for code to actually require a dict over a more
     # generic mapping. If it did, this would work fine.
-    meta: MutableMapping[MetaKey, MetaValue]
+    meta: MutableMapping[MetaKey, MetaValue]  # type:ignore[assignment]
 
 
 def iter_postings(txn: Transaction) -> Iterator[Posting]:
@@ -103,5 +103,6 @@ def iter_postings(txn: Transaction) -> Iterator[Posting]:
         yield Posting(
             Account(source.account),
             *source[1:5],
-            PostingMeta(txn, index, source),
+            # see rationale above about Posting.meta
+            PostingMeta(txn, index, source), # type:ignore[arg-type]
         )

conservancy_beancount/plugin/__init__.py

@@ -56,7 +56,8 @@ class HookRegistry:
             self.group_name_map.setdefault(key, set()).add(hook_cls)
         return hook_cls  # to allow use as a decorator
 
-    def import_hooks(self, mod_name, *hook_names, package=__module__):
+    # This method is too dynamic to typecheck.
+    def import_hooks(self, mod_name, *hook_names, package=__module__):  # type:ignore
         module = importlib.import_module(mod_name, package)
         for hook_name in hook_names:
             self.add_hook(getattr(module, hook_name))