fix: make close() sync (motor close is sync); guard doc[key] on missing fields

close() was async but only called motor's synchronous client.close(), misleading callers into awaiting it; it is now a plain def and the docstring + README examples drop the await. get_document_hashmap/get_document_fields indexed doc[key] unguarded, so a doc missing the field raised KeyError that the broad except swallowed, conflating 'no documents' with 'field absent'; both now skip docs lacking the key.

Signed-off-by: disqualifier <dev@disqualifier.me>

README.md

@@ -28,7 +28,7 @@ from mongo import Mongo
 
 db = Mongo(conn_string, database)          # attach as bot.db / app.db
 users = await db.get_documents("users", {"active": True})
-await db.close()                            # on shutdown
+db.close()                                  # on shutdown (sync)
 ```
 
 **Module proxy (back-compat)** — arm once, then call bare:

src/mongo/mongo.py

@@ -5,7 +5,7 @@ object (preferred), one client per process:
     from mongo import Mongo
     bot.db = Mongo(conn_string, database)
     await bot.db.get_documents("users", {"active": True})
-    await bot.db.close()                      # on shutdown
+    bot.db.close()                            # on shutdown (sync)
 
 module proxy (back-compat), arm once then call bare:
     import mongo                              # not `from mongo import ...`
@@ -61,8 +61,8 @@ class Mongo:
             log.exception("db.ping()")
             return False
 
-    async def close(self) -> None:
-        """close the client pool on shutdown"""
+    def close(self) -> None:
+        """close the client pool on shutdown (sync — motor's close() is synchronous)"""
         self._client.close()
 
     # -------------------------------------------------------------------------
@@ -184,7 +184,7 @@ class Mongo:
         """return matching documents keyed into a dict by the given field"""
         try:
             cursor = self._db[collection].find(target)
-            return {doc[key]: doc async for doc in cursor}
+            return {doc[key]: doc async for doc in cursor if key in doc}
         except Exception:
             log.exception(f"db.get_document_hashmap() on {collection}")
             return {}
@@ -195,7 +195,7 @@ class Mongo:
         """return a flat list of one field's value across matching documents"""
         try:
             cursor = self._db[collection].find(target, fields)
-            return [doc[key] async for doc in cursor]
+            return [doc[key] async for doc in cursor if key in doc]
         except Exception:
             log.exception(f"db.get_document_fields() on {collection}")
             return []