Add EVP digest context serialization

Add EVP digest context serialization

This commit introduces two new functions, EVP_MD_CTX_serialize and
EVP_MD_CTX_deserialize, to the EVP digest API.

These functions allow an application to save the state of a digest
context (EVP_MD_CTX) and restore it later. This is useful for
checkpointing long-running computations, enabling them to be paused
and resumed without starting over.

The implementation adds the OSSL_FUNC_DIGEST_SERIALIZE and
OSSL_FUNC_DIGEST_DESERIALIZE dispatch functions for providers to
supply this functionality.

Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/28837)