Add RISEx venue integration

[ignimbrite]

Summary

• Adds RISEx (RISE Chain mainnet perps exchange) as a new benchmarkable venue, following the existing multi-venue pattern: Go spec.Definition + Python EIP-712 signing subprocess for order placement, WS confirmation, and cleanup.
• Live-verified against RISEx mainnet end-to-end: 10/10 place → WS confirm → cancel → WS cancel-confirm cycles, repeated after fixes.
• Found and fixed two real signing bugs during live testing, not just style issues:
  • header_flags/action-hash mismatch that made every real order fail signature verification (SignerNotAuthorized).
  • A nonce-anchor caching race between the place and cleanup processes — confirmed necessary via an A/B test (reproduced the original failure with the fix reverted and the account's other live trader stopped, then confirmed the fix resolves it).
• Batch scenario is refused outright (SystemExit, HTTPBatch: false) rather than faked: RISEx's strict sequential nonce_anchor makes the usual concurrent-fanout workaround (used for Nado/Extended) unreliable — confirmed live (1 of 5 concurrent orders succeeded in one test). Matches edgeX's precedent for venues without a real batch endpoint.
• Adds a cleanup safety net (before_run/after_run sweep) that RISEx was missing — caught real leftover orders live during testing.
• Test coverage matches every other venue's convention: build_payload_test.py / cancel_payload_test.py, including a signature-recovery regression test verified to actually catch the header_flags bug by reintroducing it.
• Frontend: real RISEx logo/brand color, chart color.
• Account setup: RISEX_PRIVATE_KEY / RISEX_ACCOUNT_ADDRESS (address-only alternative for hardware wallets or signers already registered via RISEx's website) / RISEX_SIGNER_PRIVATE_KEY.

Test plan

• gofmt, go build ./..., go vet ./..., go test ./... all clean
• Python build_payload_test.py / cancel_payload_test.py (22 tests) pass, including offline signature-recovery checks
• Live mainnet: single-order place/WS-confirm/cancel/WS-cancel-confirm, 10/10 repeated across multiple runs
• Live mainnet: batch scenario correctly refuses before touching the account
• Live mainnet: nonce-anchor fix confirmed necessary via A/B test (bug reproduces without it, resolves with it)
• Reviewed for reuse/simplification/efficiency cleanups