refactor(eventbridge): split start_replay into phases

[vieiralucas]

Summary

`start_replay` was ~275 lines combining input parsing, destination/archive validation, event collection, replay record insertion, and per-target delivery fan-out. Extract three helpers so the outer function reads as a 70-line sequence of named phases:

• `StartReplayInput::from_body` owns the parse + validate phase (ReplayName, EventSourceArn, EventStartTime/EndTime, Destination, destination ARN shape check).
• `collect_replay_events_with_targets` walks the archive, filters events into the replay window, and fans each out against the bus's rules to collect matching targets.
• `deliver_replay_event_to_target` becomes a method on `EventBridgeService` so the per-protocol dispatch (sqs / sns / lambda / logs / states / http) is reachable as its own named helper — same shape as the SNS fan-out split in PR refactor(sns): split publish topic fan-out into subscribers + per-protocol deliverers #344.

Test plan

• `cargo fmt`
• `cargo clippy --workspace --all-targets -- -D warnings`
• `cargo test -p fakecloud-eventbridge --lib` — 60 passed
• `cargo test --workspace --exclude fakecloud-e2e --exclude fakecloud-conformance`

---

Summary by cubic

Refactored EventBridge start_replay into clear phases to improve readability and reuse without changing behavior. The outer function is now ~70 lines and preserves AWS validation order.

• Refactors
  • Added StartReplayInput::from_body for parsing and validating inputs (including destination ARN).
  • Added collect_replay_events_with_targets to filter archive events by time and match rules on the destination bus.
  • Added deliver_replay_event_to_target to encapsulate per-protocol delivery (SQS, SNS, Lambda, Logs, Step Functions, HTTP).

^{Written for commit 10616f6. Summary will update on new commits.}

[cubic-dev-ai]

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