Add CoW Protocol intent decoder

[MyTH-zyxeon]

Summary

• adds a CoW Protocol auction decoder that normalizes orderbook auction orders into Intent values
• maps CoW order fields into token in/out, sell amount, min buy amount, deadline, and receiver/owner recipient fallback
• wires the decoder into the intent module and CLI protocol selector
• adds an offline golden auction fixture with unit coverage

Validation

• cargo test: 9 passed
• cargo clippy --all-targets -- -D warnings

Closes #4

[abhicris]

Welcome to kcolbchain, @MyTH-zyxeon — glad you're here. 🌱

Here's what happens from this PR:

1. Our automated review looks for obvious issues (tests, secrets, size) within a couple of hours.
2. If it's clean and CI passes, we merge without back-and-forth.
3. If we need changes, we'll leave a specific comment — not a generic nit. Push another commit and we re-review.

While you wait:

• Run the repo's tests locally (see the repo README.md).
• Keep the PR scoped to one concern — bigger PRs land slower.
• Don't commit tokens or .env contents.

What happens after your first merge

• You're listed on https://kcolbchain.com/contributors/ (opt-out anytime via data/contributors-optout.txt).
• At 2+ merged PRs you're a Regular; at 5+ you're a Fellow — Fellows are the pool we invite first for paid research, partner-org gigs, and grant-funded work. Details: https://kcolbchain.com/docs/org-contribution-policy.html
• Looking for what to pick up next? https://kcolbchain.com/invitations/ lists open help-wanted / good-first-issue across every kcolbchain repo.

Thanks for writing the code. We're building this to last.

[abhicris]

🤖 Audit verdict: safe

Straightforward intent decoder implementation with proper error handling, tests, and no security red flags; follows established patterns in the codebase.

Audited by the kcolbchain PR pipeline. See pipeline docs.