Modernize OpenSSL digest and HMAC error handling (#2804) * Remove support for OpenSSL < 1.1.1 OpenSSL 1.1.0+ manages threading internally and no longer requires application-level locking callbacks. The init/cleanup functions (ERR_load_crypto_strings, EVP_cleanup, etc.) are no-ops since 1.1.0. - configure.ac: raise libcrypto minimum to 1.1.1, add compile-time version check using OPENSSL_VERSION_NUMBER, use DEPS_CFLAGS so non-default installations are detected correctly - openssl_auth.cpp: remove ~90 lines of dead crypto mutex infrastructure and obsolete init/cleanup calls - COMPILATION.md: document new minimum version * Use shared EVP digest helper for md5 and sha256 Extract common EVP digest logic from s3fs_md5() and s3fs_sha256() into s3fs_digest(). This replaces the deprecated EVP_MD_CTX_create/destroy with RAII-managed EVP_MD_CTX_new/free and adds error checking with OpenSSL error strings for every EVP call. The two s3fs_md5() variants (OpenSSL 1.1 and 3.0) were identical and are now unified into a single implementation. * Add shared EVP helper for file descriptor digests Introduce s3fs_digest_fd(), analogous to s3fs_digest(), to compute a message digest over a file descriptor using RAII-managed EVP_MD_CTX with error checking and OpenSSL error strings. Replace s3fs_sha256_fd() with a one-liner wrapper, removing deprecated EVP_MD_CTX_create/destroy and unchecked return values. * Replace s3fs_md5_fd() with s3fs_digest_fd() wrapper Both s3fs_md5_fd() variants (OpenSSL 3.0 and 1.1) are replaced by a one-liner delegating to s3fs_digest_fd(). This removes the USE_OPENSSL_30 ifdef, the deprecated MD5_Init/Update/Final calls, and the openssl/md5.h include. * Remove USE_OPENSSL_30 build flag The openssl_auth.cpp digest functions no longer have separate code paths for OpenSSL 3.0 vs 1.1, making the USE_OPENSSL_30 compile-time flag unused. Remove the version detection in configure.ac, the AM_CONDITIONAL, and the -D flag in Makefile.am. * Add error handling to HMAC call HMAC() returns nullptr on failure, but the return value was not checked. Add the missing check with an OpenSSL error message. Also add a debug message for null parameter validation and simplify the duplicated HMAC() call by selecting the algorithm upfront.