Refactors out `unsafe` from MmapAccountHashesFile::read() (#33266) #5

Job	Run time
test	0s
cargo-test-sbf (token/program)	13m 5s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	20m 57s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	17m 18s
check	0s
cargo-test-sbf (token-upgrade/program)	16m 19s
cargo-test-sbf (feature-proposal/program)	13m 2s
cargo-test-sbf (governance/addin-mock/program, governance/program)	20m 3s
cargo-test-sbf (memo/program)	13m 0s
cargo-test-sbf (name-service/program)	12m 45s
cargo-test-sbf (stake-pool/program)	20m 40s
cargo-test-sbf (single-pool/program)	20m 36s
	2h 47m 45s

Provide feedback