Removing saturating_add_assign and replacing with Saturating struct #14904

Job	Run time
cargo-test-sbf (token/program)	7m 6s
check	3m 6s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	13m 14s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	11m 7s
test (token/cli, token/program, token/program-2022, associated-token-account/program, instruction...	15m 32s
cargo-test-sbf (token-upgrade/program)	7m 33s
test (single-pool/cli, single-pool/program)	14m 42s
cargo-test-sbf (feature-proposal/program)	7m 27s
test (token-upgrade/cli, token-upgrade/program)	13m 49s
cargo-test-sbf (governance/addin-mock/program, governance/program)	11m 38s
cargo-test-sbf (name-service/program)	7m 11s
cargo-test-sbf (stake-pool/program)	10m 52s
cargo-test-sbf (single-pool/program)	7m 58s
	2h 11m 15s

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