* refactor(crypto): deprecate custom sha256 in favor of OpenSSL libcrypto
- Remove standalone src/foundation/sha256.cc, include/mocktail/sha256.h, and tests/sha256_test.cc
- Remove mocktail_crypto_foundation library and sha256_test targets from CMake
- Export clean FileDigest and HashText helpers via include/update/payload_integrity.h
- Deduplicate byte-to-hex formatting across host ABI loader and updater modules
- Support direct generation hash sizing to avoid repetitive string slicing
- Validate all EVP return codes across streaming downloads and asset tree hashing
* fix(compat): abort candidate canary registration when profile hashing fails
- Return Failure before profile validation and registration if ComputeSha256Hex fails
- Propagate canary attestation hashing failures in ValidateCanaryAttestation
- Add SetHostAbiProfileHashingFaultForTesting hook and regression test in host_abi_profile_test
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Co-authored-by: glook9001 <310372091+glook9001@users.noreply.github.com>
