refactor(migration-canister): cache last event for every migration #2850

Job	Run time
CI PR Only / Quick Feedback Tests	2m 29s
CI PR Only / Candid compatibility checks	3m 9s
CI PR Only / Lock Generate	1m 1s
CI PR Only / Generate Config Fixtures	1m 32s
CI PR Only / Bazel Build Fuzzers Archives	1m 42s
CI Main / Bazel Run Fuzzers	7m 27s
CI Main / Bazel Test arm64-linux	13m 13s
CI PR Only / Dependency Scan for PR	10s
CI Main / Set Config	3s
CI Main / Python CI Tests	1m 12s
CI Main / Cargo Build Linux	10m 18s
CI Main / Check PULL_REQUEST_BAZEL_TARGETS	22s
CI Main / Cargo Lint Linux	7m 52s
CI Main / Bazel Test arm64-darwin	9m 8s
CI Main / pocket-ic-tests-windows / Check Run PocketIC Tests	4s
Post Required Check Status Merge Queue	0s
CI PR Only / Bazel Test Coverage	0s
CI Main / Bazel Test All	24m 44s
CI Main / Bazel Test macOS Intel	3m 1s
CI Main / Build IC	13m 51s
CI Main / Bazel Build All No Cache	0s
CI Main / pocket-ic-tests-windows / PocketIC Lint on Windows	0s
CI Main / pocket-ic-tests-windows / Bazel Build PocketIC	0s
CI Main / pocket-ic-tests-windows / PocketIC Tests on Windows	0s
CI PR Only Post Required Check Status	11s
CI Main / Upload external artifacts	0s
CI Main / Build Determinism	4s
CI Main Required Check Status	10s
	1h 41m 43s

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