fix: harden exception handling, break ARC cycles, sync license/client

Replace bare except: with CatchableError across storage, query, Raft,
backup, and protocol code so Defects are not swallowed. Break uncollectable
ARC cycles in server shard/gossip callbacks via Server-owned refs and
cursor locals. Align package license with LICENSE (BSD-3-Clause), sync
README version, and point test_all at the canonical clients/nim baradb
client (parseConnectionString + aliases).

src/barabadb/query/udf.nim

@@ -211,7 +211,7 @@ proc registerStdlib*(reg: UDFRegistry) =
       if args.len > 0 and args[0].kind == vkString:
         try:
           return Value(kind: vkInt64, int64Val: parseInt(args[0].strVal))
-        except:
+        except CatchableError:
           discard
       return Value(kind: vkNull))