Add an assertion to prevent dynamic lookups without selectors/fixed

[CPerezz]

This would prevent errors like PSE-ZKEVM dynamic lookups to happen unnoticed.

[davidnevadoc]

Can you provide some explanation/ example of this error @CPerezz ? Thanks!

[jonathanpwang]

Here is an example: the diff of the PR shows what changed, and there is a RAM example test. https://github.com/axiom-crypto/halo2-lib/pull/206