Fixes #1197

Summary

• When no keys match the given Condition, ConditionalPick previously returned Pick<Base, never> which resolves to {} (empty object type). This allowed any properties to be assigned without type errors.
• Now it checks if ConditionalKeys returns never using IsNever, and returns never in that case.
• Added test cases to verify the never return behavior.

Note

The same issue exists in ConditionalPickDeep — tracked separately in #1358.