refactor(eventbridge): bundle fire_rule context refs into FireRuleContext

[vieiralucas]

Summary

`fire_rule` took 7 positional args (state + delivery + lambda_state + logs_state + container_runtime + bus_name + rule_name). Bundle the five that are "where the surrounding services live" into a borrowed `FireRuleContext<'a>`; keep `bus_name` and `rule_name` as regular params since they're the actual lookup keys, not context. Same shape as the SNS `TopicFanoutContext` from PR #344.

Updates the three unit tests in `simulation.rs` and the server's `/_fakecloud/eventbridge/fire-rule` handler in `main.rs` to construct the context inline.

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`

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Summary by cubic

Bundled the environment args for fire_rule into a borrowed FireRuleContext to simplify call sites and match the SNS TopicFanoutContext. No behavior changes.

• Refactors
  • Replaced five positional refs with FireRuleContext<'a>; kept bus_name and rule_name as parameters.
  • Updated unit tests and the server /_fakecloud/eventbridge/fire-rule handler to construct the context inline.

^{Written for commit b9fc560. Summary will update on new commits.}

[cubic-dev-ai]

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