Blockstore: Migrate ShredIndex type to more efficient data structure #16171

Job	Run time
cargo-test-sbf (associated-token-account)	1m 31s
test_cli (single-pool)	1m 31s
cargo-test-sbf (feature-proposal)	1m 30s
check (associated-token-account)	1m 19s
cargo-test-sbf (instruction-padding)	1m 31s
test_cli (token-2022)	1m 28s
check (feature-proposal)	1m 30s
cargo-test-sbf (memo)	1m 21s
check (instruction-padding)	1m 30s
check (memo)	1m 16s
cargo-test-sbf (record)	1m 30s
check (record)	1m 5s
cargo-test-sbf (single-pool)	1m 30s
cargo-test-sbf (slashing)	1m 29s
check (single-pool)	1m 29s
cargo-test-sbf (stake-pool)	1m 30s
check (slashing)	1m 14s
cargo-test-sbf (token-2022)	1m 30s
check (stake-pool)	1m 24s
check (token-2022)	1m 29s
	28m 37s

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