fix(riscv): reject reserved JALR funct3 in the lifter

[carlosqwqqwq]

fix(riscv): reject reserved JALR funct3 in the lifter

Closes #219

Summary

JALR's funct3 field is reserved and must be 0; the SMIR lifter lifted any funct3 value as a JALR. It now returns InvalidEncoding for the reserved values.

Validation

• Regression covers funct3=001 (must be rejected) and funct3=000 (must lift).
• cargo test --lib: 1 new test passes.

Notes

Independent encoding-validation root cause, distinct from the no-C alignment handling.

[19h]

I reviewed the focused commit 2a1dddb6 against issue #219. Checking funct3 == 0 at the JALR lifter boundary and returning InvalidEncoding for the reserved values matches the direct decoder and the base ISA encoding.

Two changes are needed before this is merge-ready:

1. This PR still contains 55043ddc, the closed refactor(riscv): split vector semantics out of cpu.rs #202 vector-module split. Please rebase onto current master and drop that commit so the PR contains only the focused JALR change.
2. The new regression has duplicate adjacent #[test] attributes. The focused filter runs the same test twice (2/2 with the identical name); please remove one marker.

The legal/reserved controls otherwise pass. This fix is non-RVV and should remain separate from #203.

[19h]

Thank you @carlosqwqqwq for identifying the reserved JALR funct3 gap and proposing a fix. We independently reimplemented and validated all eight field values in #231, where this is consolidated with #218, #222, and #224. No commits from this branch were taken. To keep review and CI on one maintained branch, I’m closing this PR as superseded by #231. You are credited as co-author on the consolidation commit—please review #231.