Align Yul interpreter with Solidity semantics

[danrobinson]

Summary

This aligns several Yul interpreter behaviors with Solidity's Yul semantics:

• switch now executes only the selected case body, or the default body when no case matches.
• Switches without an explicit default now lower through the Yul notation layer as an empty default body, matching Solidity's default {} equivalence.
• Block execution now drops locals declared inside the block when the block exits.
• Declarations and assignments are represented separately, so let x := ... and x := ... no longer have the same AST/semantics.
• Invalid references to out-of-scope or undeclared variables now produce an interpreter error instead of silently reading a value.
• Duplicate declarations of visible variables now produce an interpreter error, matching Solidity/Yul's no-shadowing rule.
• Function return variables are initialized to zero when a Yul function call starts.
• Call-like builtins now treat a reverted callee as a failed call returning 0, instead of propagating Revert as an interpreter error.
• Yul SELFDESTRUCT now halts execution after applying the existing modelled account and substate effects.

This does not attempt to fully remodel SELFDESTRUCT. The existing limitations around account/external-interaction behavior remain, including not triggering fallback behavior on a recipient contract and not claiming a full account-lifecycle model for all post-Cancun/EIP-6780 cases.

Regression tests

Added focused Yul semantics tests covering:

• a selected switch case with a reverting default branch;
• omitted-default switch notation lowering to an empty default and executing regularly on no match;
• block-local variables not leaking outside their block;
• rejection of shadowed declarations;
• assignment to an existing local;
• rejection of assignment to an undeclared local;
• zero initialization of empty function return variables;
• call to a reverting callee returning 0;
• SELFDESTRUCT preventing following code from executing.

Testing

lake build EvmYul.Yul.YulNotation
lake build EvmYul.Yul.YulSemanticsTests.Main
lake exe yulSemanticsTests
lake build