feat: unlock acct for auto-signing if alias resolves to KeyfileAccount

[fubuloubu]

What I did

This PR add a small UX enhancement where acct.set_autosign(True) is automatically called if a KeyfileAccount is provided for the alias. This will assist testing in local scenarios for rapid prototyping with a local wallet.

fixes: #90

How to verify it

$ silverback run example:app --network ethereum:mainnet
...  # runs just fine without a signer

$ silverback run example:app --network ethereum:mainnet --account <my-keyfile-alias>
INFO: Loading Silverback App with settings:
  APP_NAME="bot"
  ...
Enter passphrase to permanently unlock 'my-keyfile-alias':
WARNING: Danger! This account will now sign any transaction it's given.
SUCCESS: Loaded Silverback App:
  NETWORK="ethereum:mainnet"
  SIGNER=<KeyfileAccount address=0x...  alias=dev >
INFO: Using WebsocketRunner: max_exceptions=3
...

Checklist

• Passes all linting checks (pre-commit and CI jobs)
  - [ ] New test cases have been added and are passing
• Documentation has been updated
• PR title follows Conventional Commit standard (will be automatically included in the changelog)

[mikeshultz]

LGTM