riscv-opcodes snapshot for the Digital Design Studio RISC-V import

Upstream: https://github.com/riscv/riscv-opcodes
Commit: 5783cf3bea312a48d28e3e2c8a2fcb55603e4bed (2026-09-18T00:35:48-07:00)
License: BSD-3-Clause; LICENSE is the verbatim upstream file.

The files under extensions/ and the *.csv tables are unmodified copies of the
upstream commit, limited to the first import scope (RV32I/RV64I + M, A, F, D, C,
Zicsr, Zifencei). generated/ holds output of the upstream generator run on the
same commit; it is derived data under the same license. source.json records the
SHA-256 digest and git blob id of every file and the complete upstream
extensions/ inventory.
