fix: use cryptographic RNG for order salt

[deipeypaanchal]

Summary

• generate_order_salt was int(random.random() * current_ms_time):
  • random.random() is not cryptographic.
  • The result is always strictly less than current_ms_time, so the salt is not uniformly distributed.
  • Concurrent order creation in the same millisecond can produce duplicate salts, which the exchange rejects as duplicate orders.
• Switch to secrets.randbits(64) — 64 bits of uniform cryptographic entropy, well within the uint256 salt field.

Test plan

• Generate a few thousand salts back-to-back and confirm no duplicates.
• End-to-end order placement still succeeds.

🤖 Generated with Claude Code

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Note

Low Risk
Small, localized change to salt generation; low risk aside from potential downstream assumptions about salt format/range.

Overview
generate_order_salt now uses secrets.randbits(64) instead of a random.random() * time-based value, improving entropy, uniformity, and reducing collision risk during concurrent order creation.

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