feat(debugger): auto-sign sig args from secret keys

[atl4so]

Summary

Adds optional 32-byte secret-key auto-signing for sig arguments in cli-debugger .test.json fixtures.

If a sig argument is supplied as 32 bytes, the debugger now materializes it into a real Kaspa Schnorr signature over the test transaction sighash with SIG_HASH_ALL. Existing fixtures that pass raw 65-byte signatures continue to work unchanged. Includes argument offset handling for covenant functions where synthesized prefix args (State prev_state, State[] next_states) shift user-callable parameter positions.

Motivation

Upstream Rust tests can exercise signature flows by calling the Kaspa signing libraries directly and embedding raw signature bytes. External tooling that drives cli-debugger through .test.json cannot do that without reimplementing transaction signing outside the debugger.

This gives JSON-driven tools, fuzzers, and audit generators a deterministic way to produce signed fixtures from synthetic keys while still executing the real script path in cli-debugger.

Testing

• cargo test -p cli-debugger

Added an integration test covering:

• valid 32-byte secret key -> materialized Schnorr signature passes checkSig
• wrong 32-byte secret key -> materialized signature fails checkSig
• covenant function with sig param after synthesized prefix args -> secret key offset correctly, materialized signature passes checkSig