fix pack checksum handling for sha256

zero also base_id in search_delta_for_object not sure why it's needed, it should be zeroed by got_pack_parse_ref_delta via got_packfile_extract_raw_delta, but it isn't.

fix fallout; mostly struct got_object_id zeroing

bump hash size and add algo field to got_object_id; fix a few places

handle repository format version 1 and objectformat extension

add field to got_packidx to propagate the hash algo allows to drop all the `algo' hardcodings in lib/pack.c and pack_idx.c

handle both sha1 and sha256 object ids in pack files bump got_packidx_object_id so it can hold a sha256 digest and adapt the code to read the needed type of hash.

add an hash algo field to got_pack - maybe useless

bubble up the algo argument

adjust GOT_PACKIDX_NAMELEN for sha256 packs

rename pack{file,idx}_sha1 to _hash

rename "sha1" field to "hash" done with X ,x/\.sha1/c/hash X ,x/->sha1/c/->hash in sam after loading all the C files; except for one manual tweak in hash.c

add got_repo_get_object_format() ...and use it to avoid hardcoding the algo in a few places.

inflate: support sha256

introduce more helpers to deal with different hash digests