feat: rv64 alu_w shift_w

[876pol]

Resolves INT-6340, INT-6343.

Summary:

• base_alu_w and shift_w reuse the existing generic core AIRs (BaseAluCoreAir<RV64_WORD_NUM_LIMBS, RV64_CELL_BITS> and ShiftCoreAir<RV64_WORD_NUM_LIMBS, RV64_CELL_BITS>) via type aliases, eliminating the need for duplicated core code.
• A new Rv64BaseAluWAdapter (alu_w.rs) bridges 64-bit register memory with the 4-byte core interface: it reads full 8-byte registers but only passes the low 4 bytes to the core, and sign-extends the 4-byte core output back to 8 bytes on write.
• The test suite is largely carried over from the original RV32 code and primarily exercises the reused core AIR logic rather than the newly written adapter.