feat: add explicit backrun bundle cancellation via 0-tx submissions

[dvush]

📝 Summary

Sending eth_sendBackrunBundle with 0 transactions, a replacementUuid, and a replacementNonce cancels the active bundle for that UUID. The cancellation uses the same nonce semantics as replacements: strictly higher nonce wins.
Cancellations expire after CANCELLATION_MAX_BLOCK_RANGE=2 blocks.

💡 Motivation and Context

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✅ I have completed the following steps:

• Run make lint
• Run make test
• Added tests (if applicable)

[Copilot]

Pull request overview

This PR adds explicit backrun bundle cancellation support via 0-transaction eth_sendBackrunBundle submissions. When a caller sends a bundle with 0 transactions along with a replacementUuid and replacementNonce, the active bundle for that UUID is removed from all block payload pools. The same strictly-higher-nonce semantics used for bundle replacements apply to cancellations. Cancellation entries expire after CANCELLATION_MAX_BLOCK_RANGE (2) blocks from the current tip.

Changes:

• Introduces UuidEntry enum (Bundle | Cancellation) to unify bundle and cancellation state under the same per-UUID tracking map in the global pool, adds cancel_bundle public API, and refactors repeated pool insertion/removal logic into helpers.
• Adds cancellation path in the send_backrun_bundle RPC handler: routes 0-tx submissions to cancel_bundle, returning B256::ZERO as the bundle hash.
• Adds unit tests (test_cancellation, extended test_on_canonical_state_change) and an integration test (backrun_cancellation), along with a send_backrun_cancellation test helper.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
crates/op-rbuilder/src/backrun_bundle/global_pool.rs	Introduces UuidEntry enum, cancel_bundle method, remove_bundle_from_pools/insert_bundle_into_pools helpers, and updated canonical state cleanup.
crates/op-rbuilder/src/backrun_bundle/rpc.rs	Adds the 0-tx cancellation path in send_backrun_bundle and removes the now-obsolete 0-tx rejection test case. Adds test_cancel_requires_uuid_and_nonce.
crates/op-rbuilder/src/tests/framework/txs.rs	Adds send_backrun_cancellation test helper.
crates/op-rbuilder/src/tests/backrun.rs	Adds backrun_cancellation integration test.

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[avalonche]

is there a test for cancellations expiring after CANCELLATION_MAX_BLOCK_RANGE?

[dvush]

cancellation expiration is tested here https://github.com/flashbots/op-rbuilder/pull/423/changes#diff-bb1901a42309ca5fa0a7f7ad29c0fadcbd36b7cf6e9460791a94dffd85fb4855L336