feat: add packageIdSelectionPreference and rework batch-delete example

[scolear]

What

Adds a packageIdSelectionPreference field to Submission and reworks the
delete_executed_transfers example to use it.

This is the work-in-progress that was sitting uncommitted on the old
I11-endpoint-migration branch. The endpoint migration itself already landed on
main (squash-merged as #13), so this PR carries only the remaining follow-on
changes, replanted onto current main.

Changes

common

• Add Submission.package_id_selection_preference (serialized as
  packageIdSelectionPreference, omitted when empty). Lets callers pin Canton's
  package-name resolution to specific package hashes instead of relying on its
  default smart-upgrade selection — needed when a participant has multiple vetted
  versions of a package and the choice you need only exists in one of them.

examples/delete_executed_transfers

• Call CBTCGovernanceRules_BatchDeleteExecutedTransfers.
• Pass RegistrarService as a choice argument with read-as visibility on the
  decentralized party — no disclosed_contracts blob required.
• New PACKAGE_ID_PREFERENCE env var, fed into packageIdSelectionPreference.
• Configurable BATCH_SIZE with automatic bisection on PACKAGE_SELECTION_FAILED
  (a failed batch is split in half and retried, so a few bad contracts don't sink
  the whole batch).
• Append successfully-processed and individually-failed contract IDs to CSV files
  (PROCESSED_CSV / FAILED_CSV) for safe, resumable re-runs.

Replant notes

Rebased cleanly onto current main; verified the following improvements that
main made after the WIP's base were preserved (not reverted):

• keycloak token_url(.../auth, realm) (feat(keycloak): added Quarkus-style token URL helpers #19)
• div_ceil clippy fixes for chunk/batch sizing
• the flat submit::wait_for_transaction endpoint

Verification

• cargo clippy -p examples -p common --all-targets — clean, no warnings.
• cargo fmt was not run repo-wide: main is not rustfmt-clean (23 dirty
  files under the pinned toolchain) and there's no fmt CI gate. Only the reworked
  example file was formatted, to keep this diff focused.