Similar to from_v3_gced. New fields:

latest_gc_target_offset is the commit on which the latest gc was called on.

suffix_dead_bytes is the number of bytes at the beginning of the suffix that should be considered unreachable after a GC.

From_v1_v2_post_upgrade similar to Payload_v3.From_v1_v2_post_upgrade

No_gc_yet corresponds to a pack store that was created using `V3 or above. It never underwent a GC.

Used_non_minimal_indexing_strategy corresponds to a pack store that was created using `V3 or above. It never underwent a GC and it will never be possible to GC it because entries were pushed using a non-minimal indexing strategy.

Gced is a `V3 or `V4 store that was GCed at least once.

The T* tags are provisional tags that the binary decoder is aware of and that may in the future be used to add features to the `V4 payload.

The same as Payload_v3.t, with the following modifications:

New fields

• upgraded_from_v3_to_v4 recalls if the store was originally created in `V3.
• chunk_start_idx is the index for the starting chunk of the suffix
• chunk_num is the number of chunks in the suffix
• checksum for storing a checksum of the payload
• appendable_chunk_poff is a value used by the chunked suffix. See Chunked_suffix.S.appendable_chunk_poff for more details.

Removed fields

• suffix_end_poff is replaced by appendable_chunk_poff