a056fd88cb
* uses Option<Slot> for SlotMeta.parent_slot (#21808)
SlotMeta.parent_slot for the head of a detached chain of slots is
unknown and that is indicated by u64::MAX which lacks type-safety:
https://github.com/solana-labs/solana/blob/6c108c8fc/ledger/src/blockstore_meta.rs#L203-L205
The commit changes the type to Option<Slot>. Backward compatibility is
maintained by customizing serde serialize/deserialize implementations.
(cherry picked from commit 8d980f07ba)
# Conflicts:
# ledger-tool/src/main.rs
* removes backport merge conflicts
Co-authored-by: behzad nouri <behzadnouri@gmail.com>