Add zero-denominator guards to SMOD, ADDMOD, MULMOD

[Copilot]

SMOD, ADDMOD, and MULMOD were missing zero-denominator checks required by EVM spec. Per spec, these operations must return 0 when the denominator is 0.

Changes

• ops.rs: Added zero guards to smod(), addmod(), and mulmod() following existing DIV/MOD pattern
• test_roms.rs: Added tests verifying zero-denominator behavior

Implementation

Uses LLVM select to conditionally return zero:

let zero = bctx.env.types().i256.const_zero();
let c_is_zero = bctx.builder.build_int_compare(
    inkwell::IntPredicate::EQ, c, zero, "c_is_zero"
)?;

let mod_result = bctx.builder.build_int_unsigned_rem(result, c, "mod_result")?;
let result = bctx.builder.build_select(c_is_zero, zero, mod_result, "final")?;

This matches the pattern already used by DIV (line 381) and MOD (line 411).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>SMOD/ADDMOD/MULMOD need to guard on 0</issue_title>
<issue_description>SMOD/ADDMOD/MULMOD Must check for the second argument being a zero, and if so, should use zero as the result of the entire operation. This is currently done in DIV, for reference.

Originally posted by @Copilot in #48 (comment)
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes SMOD/ADDMOD/MULMOD need to guard on 0 #51

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[semanticdiff-com]

Review changes with  

Changed Files

File	Status
crates/jet/src/builder/ops.rs	21% smaller
crates/jet/tests/test_roms.rs	0% smaller