Uses `IntSet` for `ShrinkCandidates` #2123

Job	Run time
cargo-test-sbf (token/program)	3m 31s
cargo-test-sbf (token/program)	3m 31s
check	0s
check	0s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	4m 51s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	4m 51s
test	0s
test	0s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	5m 46s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	5m 46s
cargo-test-sbf (token-upgrade/program)	3m 4s
cargo-test-sbf (token-upgrade/program)	15m 25s
cargo-test-sbf (feature-proposal/program)	5m 8s
cargo-test-sbf (feature-proposal/program)	5m 8s
cargo-test-sbf (governance/addin-mock/program, governance/program)	4m 51s
cargo-test-sbf (governance/addin-mock/program, governance/program)	4m 51s
cargo-test-sbf (memo/program)	4m 30s
cargo-test-sbf (memo/program)	4m 30s
cargo-test-sbf (name-service/program)	3m 56s
cargo-test-sbf (name-service/program)	3m 56s
cargo-test-sbf (stake-pool/program)	4m 10s
cargo-test-sbf (stake-pool/program)	4m 10s
cargo-test-sbf (single-pool/program)	4m 21s
cargo-test-sbf (single-pool/program)	4m 21s
	1h 40m 37s

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