fix(app): correct enqueue_many middleware args and option propagation

[pratyush618]

Summary

P0-3 from the pre-release audit. enqueue_many had three bugs in the on_enqueue middleware dispatch that the test suite was missing entirely:

1. Always passed args_list[0] and kw_list[0] to every middleware call, so middleware could not distinguish jobs in the batch.
2. Created a fresh empty options dict per call that was never read back, so any option mutations (priority, queue, delay, …) were silently discarded.
3. Bare except: pass swallowed middleware exceptions with no logging.

The fix restructures the dispatch to match single-enqueue's contract: per-job options dict initialised from the call-site arguments, middleware runs before enqueue_batch so mutations can take effect, mutated values are read back into the per-job lists.

What changed

• py_src/taskito/app.py — enqueue_many() rewritten to:
  • Build a per-job options dict from the call-site arguments (uniform priority/queue/etc. broadcast across the batch; per-job lists threaded through).
  • Run on_enqueue middleware against each per-job dict before enqueue_batch, replacing the silent except: pass with logger.exception("middleware on_enqueue() error").
  • Read the mutated dict back into per-job lists for the Rust call.
• crates/taskito-python/src/py_queue/mod.rs — enqueue_batch signature widened from Option<Vec<i32>> to Option<Vec<Option<i32>>> for priorities / max_retries_list / timeouts. Matches the existing pattern already used for delay_seconds_list / metadata_list / expires_list / result_ttl_list. Allows middleware to set per-job priority while letting other jobs fall back to queue defaults.
• py_src/taskito/_taskito.pyi — type stub follows the Rust signature change.

Tests

Three new regression tests in tests/python/test_batch.py:

• test_enqueue_many_invokes_on_enqueue_per_job — middleware sees each job's own args/kwargs.
• test_enqueue_many_applies_option_mutations — middleware mutating options["priority"] per-job propagates to the actual jobs.
• test_enqueue_many_logs_middleware_exceptions — exceptions from misbehaving middleware are logged via logger.exception and don't block the enqueue.

Test plan

• cargo test --workspace — 89 pass
• cargo clippy --workspace --all-targets -- -D warnings clean
• cargo check --features postgres clean
• cargo check --features redis clean
• uv run python -m pytest tests/python/ — 488 pass, 9 skipped (was 485, +3 new)
• uv run ruff check py_src/ tests/ clean
• uv run mypy py_src/taskito/ clean
• CI green