fix: hasSingleUnnamedParam incorrectly matching named parameters

The hasSingleUnnamedParam function was only checking the parameter type
but not whether the parameter actually had no name. This caused functions
with a single NAMED parameter (e.g., `foo(data json)`) to incorrectly
match the single-param fallback mode.

The result was a confusing PostgreSQL error 42883 "function does not exist"
instead of a clean PGRST202 error explaining that no matching function
was found.

Added ppName == mempty check so functions with named parameters don't
incorrectly match the single-param fallback.

test/spec/fixtures/schema.sql

@@ -2356,6 +2356,11 @@ create or replace function test.unnamed_json_param(json) returns json as $$
   select $1;
 $$ language sql;
 
+-- Function with a NAMED json parameter (for testing single param fallback behavior)
+create or replace function test.named_json_param(data json) returns json as $$
+  select data;
+$$ language sql;
+
 create or replace function test.unnamed_text_param(text) returns "text/plain" as $$
   select $1::"text/plain";
 $$ language sql;