test: integration tests for reorg tracking in RPC subscriptions and filters

[prestwich]

Summary

• Adds 7 integration tests in crates/node-tests/tests/reorg.rs verifying end-to-end reorg handling across the RPC layer
• Tests cover block tag rewind, polling filter watermark reset, push subscription removed: true log emission, filter selectivity during reorgs, and a no-regression check
• Uses host system transactions (simple_transact) to avoid tx pool conflicts on block rebuild after revert

Closes ENG-1972

Stack

This PR includes commits from #96, #97, and #98. Review only the top commit.

1. feat: update BlockTags during reorgs to prevent stale tag window #96 — BlockTags::rewind_to for reorg tag updates
2. feat: handle ChainEvent::Reorg in SubscriptionTask #97 — SubscriptionTask reorg handling
3. feat: handle reorgs in get_filter_changes with reorg watermark #98 — get_filter_changes reorg watermark
4. test: integration tests for reorg tracking in RPC subscriptions and filters #99 ← this PR — Integration tests

Test plan

• cargo clippy -p signet-node-tests --all-features --all-targets — clean
• cargo +nightly fmt — clean
• cargo t -p signet-node-tests --test reorg — 7/7 pass
• cargo t -p signet-node-tests — full suite passes, no regressions

🤖 Generated with Claude Code

[Fraser999]

LGTM (one non-blocking nitpick), but claude has made a couple of points:

• No multi-block reorg test for filters/subscriptions:
  All filter and subscription reorg tests only revert a single block. test_block_tags_reorg does a 2-block revert, but without filters or subscriptions active. A test that reverts 2+ blocks while a log filter/subscription is active would exercise the watermark.min() path and deeper reorg recovery.

• No test for multiple reorgs between polls:
  set_reorg_watermark uses min() to keep the deepest watermark when multiple reorgs arrive before a single poll. This behavior is untested.

I'm not convinced either of these are actually worthwhile actioning though, so approving as is, and you can decide whether to add these cases or not.

[prestwich]

[Claude Code]

Addressed all review feedback in 8859bfe:

1. assert_eq! nitpick — now fetches the actual block 3 hash and asserts equality instead of assert_ne!.

2. Multi-block reorg tests — added test_multi_block_reorg_log_filter (reverts 3 blocks with active log filter) and test_multi_block_reorg_log_subscription (reverts 2 blocks with active log subscription, verifies removed: true emission per block).

3. Multiple reorgs between polls — added test_multiple_reorgs_between_polls: two separate reorg-rebuild cycles without polling between them, where the second reorg is deeper. Validates that set_reorg_watermark's min() keeps the deeper watermark, causing correct re-delivery from block 4 onward.

All 10 reorg tests pass.