Use checked math for `_new_from_parent` (#2859) #8

Job	Run time
cargo-test-sbf (token/program)	12m 26s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	20m 14s
check	5m 42s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	15m 5s
cargo-test-sbf (token-upgrade/program)	11m 34s
test (token/cli, token/program, token/program-2022, associated-token-account/program, instruction...	24m 19s
cargo-test-sbf (feature-proposal/program)	12m 31s
test (single-pool/cli, single-pool/program)	20m 3s
cargo-test-sbf (governance/addin-mock/program, governance/program)	26m 17s
test (token-upgrade/cli, token-upgrade/program)	26m 44s
cargo-test-sbf (memo/program)	12m 9s
cargo-test-sbf (name-service/program)	11m 59s
cargo-test-sbf (stake-pool/program)	12m 37s
cargo-test-sbf (single-pool/program)	9m 27s
	3h 41m 7s

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