feat(bundle): filter bundles with stale host tx nonces before SimCache

[init4samwise]

Summary

Adds nonce checking for host transactions in BundlePoller, following the existing TxPoller pattern.

Problem

BundlePoller ingests bundles without checking if host tx nonces are stale. Bundles with consumed nonces:

1. Get added to SimCache
2. Fail simulation with "nonce too low"
3. Get removed
4. Re-ingested on next poll (~1s)

This creates ERROR log spam and wastes simulation cycles.

Solution

Before adding bundles to the outbound channel, spawn an async task that:

1. Decodes each host transaction
2. Recovers the sender address
3. Fetches current nonce from host provider
4. Drops bundle if any host tx has stale nonce (tx_nonce < provider_nonce)

This mirrors the existing spawn_check_nonce pattern in TxPoller.

Changes

• Added spawn_check_bundle_nonces method to BundlePoller
• Added decode_tx helper function
• Updated task loop to use nonce checking before forwarding bundles
• Uses DEBUG-level logging for dropped bundles (not ERROR)

Testing

CI will run cargo check/clippy. Manual testing can verify bundles with stale nonces are filtered.

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Closes ENG-1937

[init4samwise]

[Claude Code]

Note: The ticket also mentions reducing the log level at signet-sdk driver.rs#L250 from ERROR to DEBUG. That change is in a different repo (signet-sdk) and would need a separate PR. This PR addresses the root cause by filtering stale bundles before they reach SimCache, which should eliminate the log spam at its source.