fix: remove viem from devDependencies and update lockfile

The initial commit only removed viem from peerDependencies but left it
in devDependencies. This caused the CI lockfile check to fail.

This commit:
- Removes viem from devDependencies in package.json
- Updates yarn.lock to reflect the removal

All 20 tests still pass.

Co-authored-by: jeffsmale90 <jeffsmale90@users.noreply.github.com>

Author: cursoragent

packages/x402/package.json

@@ -67,7 +67,6 @@
     "prettier": "^3.5.3",
     "tsup": "^8.5.0",
     "typescript": "5.5.4",
-    "viem": "2.31.4",
     "vitest": "^3.2.4"
   }
 }