Add LIFO and nested-block tests

Objective

Add execute tests for LIFO order in one scope and inner-before-outer order in nested scopes.

Why it was needed

gccrs already produced the expected Drop order, but the testsuite did not check it.

Later local bindings must drop before earlier ones. Values in an inner block must drop before values in the outer block.

These tests record both rules.

Test cases

• drop-local-binding-lifo.rs: Declares A, B, and C in one scope and expects C, B, A.
• drop-nested-block-scope.rs: Checks inner-scope cleanup before outer-scope cleanup and reverse order inside each scope.