fix(riscv): count only retired instructions in instret

[carlosqwqqwq]

fix(riscv): count only retired instructions in instret

Closes #232

Summary

The retired-instruction counter counts instructions that retire. An ECALL or EBREAK leaves the interpreter through a non-Continue exit and must not be counted as a normally retired instruction. The affected step() path increments instret after every successful execute() return, including Ecall and Ebreak; the JIT fallback repeated the same rule. This makes counter observations differ between an architectural guest and RAX, and can affect code using instret for profiling or progress accounting.

The fix increments instret only for Continue and Wfi exits, while preserving the existing cycle counter increment.

Validation

• Targeted test ecall_ebreak_do_not_increment_instret fails on the base checkout and passes with the fix.
• cargo test --lib: full library test suite passes with no regressions.

No new upstream test files are added; this is a source-only change.

[19h]

Thank you for reporting and proposing this fix. I independently reimplemented and validated precise instret accounting for normal completion, ECALL, EBREAK, traps, and JIT fallback in the consolidation PR #231; no commits or code from this branch were taken. The rollup carries @carlosqwqqwq as co-author on its commits and includes direct and native regression coverage. I’m closing this PR as superseded by #231—please review the consolidated implementation there.