fix: preserve bytes32 address width in auction observer

[Kewe63]

Description

• Decode bytes32-encoded Ethereum addresses by removing exactly the 12-byte ABI padding.
• Apply the fixed-width conversion to sender, recipient, inputToken, outputToken, and destinationSettler.
• Add a real-observer regression test covering leading-zero and all-zero 20-byte addresses.

Motivation and Context

ViemIntentObserver used Viem's trim() for address-valued bytes32 fields. trim() removes every leading zero byte, including bytes that belong to the 20-byte address. A valid token such as 0x00000000000000000000000000000000000000a1 therefore became 0xa1 before reaching the auction service, preventing exact token-address matching.

The new helper uses sliceHex(value, 12) to discard only the ABI padding and preserve the full address width.

Fixes #245.

Open PR #223 also modifies the observer for recovery behavior but does not address fixed-width address decoding. It currently reports mergeable: false against canary, and a pre-push merge-tree check conflicts in ViemIntentObserver.ts; this PR remains independently based on current canary.

How Has This Been Tested?

• Full serialization audit on current canary reproduced 0x0000…00a1 becoming 0xa1; ordinary-address, ABI tuple/event, and EIP-712 controls passed.
• Pre-fix regression test — 0 passed, 1 failed with expected full sender address vs received 0xa1.
• bun test test/ViemIntentObserver.address-decoding.test.ts — 1 passed, 0 failed, 5 assertions after the fix.
• Full package suite after the fix — 2 passed, 3 failed. The same three unrelated failures occur on the clean audited tree: two stale WebSocket price fixtures raise Invalid argument type in ToBigInt operation, and processIntentLogs.test.ts checks an asynchronous notification before it occurs.
• bun x tsc -p tsconfig.json --noEmit — blocked by the same pre-existing ABI event typing, WebSocket response typing, missing vitest, and stale test-signature errors on clean canary; no new diagnostic references the added regression test or fixed-width conversion.
• git diff --cached --check — passed.
• Independent code review — passed with no blocking correctness, security, typing, or hidden-regression findings.

Types of changes (remove all unchecked types)

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I assessed the documentation impact; no documentation update is required.
• I assessed the deployment-script impact; no deployment script is changed.
• I added regression coverage for every address-valued field decoded by this observer path.