fix(tracer): use wrapping_add in alignment assertions

[wstran]

Summary

VirtualAssertWordAlignment::exec and VirtualAssertHalfwordAlignment::exec
compute the effective address via cpu.x[rs1] + imm. Both operands are
i64, so the bare + panics in debug builds when the signed sum falls
outside [i64::MIN, i64::MAX]. The other 30+ memory-touching tracer
instructions (LB/LBU/LH/LHU/LW/LWU/LD, SB/SH/SW/SD, VirtualLW/VirtualSW,
AMO*) all use wrapping_add; these two are the only outliers.

Reproducer

let mut cpu = Cpu::new(Box::new(DummyTerminal::default()));
cpu.x[1] = i64::MAX;
let instr = VirtualAssertWordAlignment {
    address: 0,
    operands: FormatAssert { rs1: 1, imm: 1 },
    virtual_sequence_remaining: None,
    is_first_in_sequence: false,
    is_compressed: false,
};
let mut ram_access = ();
instr.execute(&mut cpu, &mut ram_access);
// thread '...' panicked at virtual_assert_word_alignment.rs:21:23:
// attempt to add with overflow

Why this is correct

• RV64 spec: effective addresses are rs1 + sign_ext(imm) mod 2^64
  (per the audit Finding 1 framing in Fix audit findings from 2026-04-15 report #1442).
• Codebase convention: every other memory-touching tracer instruction
  uses wrapping_add for the same operation. Verified via
  grep -rn 'as usize\] +' tracer/src/instruction/ — only these two
  files match before this fix.
• No release-mode change: signed + already wraps in release, and
  the alignment check operates on the same low bits in both forms. The
  fix only stops the spurious debug-build panic on overflow.

Test plan

• cargo fmt -q
• cargo clippy -p jolt-core --features host --message-format=short -q --all-targets -- -D warnings
• cargo clippy -p jolt-core --features host,zk --message-format=short -q --all-targets -- -D warnings
• cargo nextest run -p tracer — 114/114 pass (includes 2 new regression tests, both red on the un-fixed code)
• cargo nextest run -p jolt-core muldiv --cargo-quiet --features host — pass
• cargo nextest run -p jolt-core muldiv --cargo-quiet --features host,zk — pass

[moodlezoup]

thanks!