feat: sidecar long pending deposits management

[Jiloc]

Description

This PR adds support for handling long-pending transactions. It addresses the issue of transactions that remain in a pending state for extended periods without being confirmed in the mempool, which can lead to system bloat.

Changes

• Added long-pending transaction detection and processing to the DepositProcessor service:
• Implemented process_long_pending method to identify transactions that have been pending for too long
• Added logic to mark transactions as FAILED if they:
  - Are in PENDING status
  - Cannot be found in the mempool (likely dropped)
  - Have been pending for longer than the configured maximum time (default: 24 hours)
  - Integrated long-pending transaction processing into the main deposit update workflow
• Added MAX_UNCONFIRMED_TIME configuration setting (default: 86400 seconds / 24 hours) to control how long a transaction can remain unconfirmed before being marked as failed

Testing Information

• Added unittests
• uv run python -m unittest

Checklist:

• I have performed a self-review of my code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules