test(sdk-lib-mpc): add DKLS replay/stale-round negative tests

[mmcshinsky-bitgo]

Summary

• (TPA-08 audit follow-up): add negative tests for the DKLS (ECDSA MPCv2) signing session covering two adversarial scenarios flagged as a coverage gap:
  • round messages replayed from an independent, concurrent sign session into an unrelated session signing the same message
  • a stale round-3 message replayed into a session that has already advanced to round 4
• Both new tests confirm the wasm bindings reject these inputs (throw) rather than silently accepting them.

Test plan

• Ran modules/sdk-lib-mpc DKLS Dsg suite locally (mocha --require tsx --node-option experimental-wasm-modules, filtered via --grep): both new tests pass, along with all 11 pre-existing cases in the file.
• Ran the same suite unfiltered multiple times to check for regressions.

Note on suite-wide flakiness (not caused by this change)

While verifying, the broader sdk-lib-mpc test suite intermittently throws Uncaught Error: recursive use of an object detected which would lead to unsafe aliasing in rust from the DKLS wasm bindings' FinalizationRegistry callback. This reproduces in unrelated files (test/unit/curves/secp256k1.ts, test/unit/tss/ecdsa/dlogproofs.ts) both with and without this PR's changes — it's a pre-existing GC-timing race in the wasm session cleanup, not something introduced here. This matches a gap already called out in the architecture audit (TPA-08: "review exception paths for WASM/session cleanup... whether serialized session state is always encrypted and integrity-protected"). Flagging here for visibility; not in scope for this test-only PR.