Update dryrun ledger generation script for Mesa

[georgeee]

Update the script to make it possible to generate ledger for Mesa's ITN testing using existing set of private keys and passing the --pad-app-state flag.

Successfully generated new ledger files with:

TMPDIR=~/tmp scripts/generate-ledger-hf-dryrun.sh --output-dir ~/mesa-itn-keys-2025dec11 -p 2 -k 2 -e 1 -b 100000000 --pad-app-state --prefix itn-testbed-1

• Don't regenerate keys in generate-ledger-hf-dryrun.sh
• Add --pad-app-state flag

Explain how you tested your changes:

• [x] Executed the updated script

Checklist:

• [x] Dependency versions are unchanged
  • Notify Velocity team if dependencies must change in CI
• [x] Modified the current draft of release notes with details on what is completed or incomplete within this project
• [x] Document code purpose, how to use it
  • Mention expected invariants, implicit constraints
• [x] Tests were added for the new behavior
  • Document test purpose, significance of failures
  • Test names should reflect their purpose
• [x] All tests pass (CI will check this if you didn't)
• [x] Serialized types are in stable-versioned modules
• [x] Does this close issues? None