Support const grant-once operations

[guosran]

Summary

Addresses #292 with minimized GRANT_ONCE_CONST support. This PR updates GrantRTL.py plus shared opcode definitions in lib/opt_type.py.

Changes

• Add const-input support for grant-once operations.
• Track grant-once state per control-memory slot so independent control slots do not share state.
• Add the required shared const opcode entry.

Validation

Part of the master-based small conv passing set.

[guosran]

Grant-once with a const threshold should grant only the first matching event.

input stream: 0, 1, 1, 1
const condition: grant when input == 1

Expected output grant:
0, 1, 0, 0