Add fuzzers for sntrup #352

Job	Run time
build (plain linux, 1)	1m 1s
build (multi binary, 1, 1)	1m 3s
build (multi binary, dropbearmulti argv0, 1, 1)	1m 7s
build (client only, no, PROGRAMS=dbclient)	32s
build (server only, no, PROGRAMS=dropbear)	29s
build (bundled libtom, bionic , no writev(), ubuntu-20.04, --enable-bundled-libtom --enable-werro...	32s
build (linux clang, clang)	1m 5s
build (c89, -std=c89 -Wdeclaration-after-statement, 1, --enable-pam, #define DROPBEAR_SNTRUP761 0 )	57s
build (macos 14, macos-14, clang, -Wno-deprecated-declarations -Wno-undef, no, no, ranlib -no_war...	26s
build (macos 15, macos-15, clang, -Wno-deprecated-declarations -Wno-undef, no, no, ranlib -no_war...	34s
build (DEBUG_TRACE, 1, --enable-pam, #define DEBUG_TRACE 5 )	1m 2s
build (nondefault options, 1, --enable-pam)	1m 5s
build (most options disabled, --disable-harden --disable-zlib --disable-openpty --disable-lastlog...	1m 18s
build (no sha1, no, #define DROPBEAR_SHA1_HMAC 0 #define DROPBEAR_RSA_SHA1 0 #define DROPBEAR_DH_...	37s
build (pq, no plain x25519, #define DROPBEAR_CURVE25519 0 )	57s
	12m 45s

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