fix: resolve multi-word types when filtering functions by args

[hsusul]

Summary

• Fixes functions.create/retrieve fails for multi-word argument types #1146: functions.create / retrieve failed for args like double precision and timestamp with time zone because only the last space-separated token was cast to regtype.
• Resolve unnamed multi-word SQL types as a whole; for named args, drop the first token and cast the remainder.
• Regression test covers create + retrieve by multi-word types.

Test plan

• npx vitest run test/index.test.ts -t "create and retrieve function with multi-word|retrieve function by args filter - polymorphic|retrieve, create, update, delete"
• Studio: create a function with a double precision argument and confirm it returns successfully