feat(chain)!: Use a more granular state machine for IBD

[Davidson-Souza]

Description and Notes

Related to #1089

Instead of just true/false, this commit tells where we are on IBD. It can either be DownloadingHeaders,DownloadingBlocks or Done.

[Davidson-Souza]

Pushed 5a48287:

• Removing full paths
• Adding and updating docs
• removing unrelated change in wire

[luisschwab]

I think IBDState should be even more granular, and should also report the backfill status eg:

pub enum IBDSate {
    HeaderSync(u32), // header height

    BlockDownload(u32), // block height

    Backfill(u32), // backfill height

    Done,
}

Or maybe even:

pub enum IBDSate {
    HeaderSync(u32), // header height

    BlockDownload(u32), // block height

    Done { backfill: Option<u32> },
}

[Davidson-Souza]

I think IBDState should be even more granular, and should also report the backfill status eg:

pub enum IBDSate {
    HeaderSync(u32), // header height

    BlockDownload(u32), // block height

    Backfill(u32), // backfill height

    Done,
}

Or maybe even:

pub enum IBDSate {
    HeaderSync(u32), // header height

    BlockDownload(u32), // block height

    Done { backfill: Option<u32> },
}

Backfill is harder because it uses a partial chainstate instead of the regular one. We would need to propagate progress back to the node and into the chain to know that. The others are fine.

[Davidson-Souza]

Actually, is this really needed? You can get this from already existing methods.

Edit: if this was a notification it would make more sense

[Davidson-Souza]

Fixed a typo with the enum name.

[moisesPompilio]

I think this comment needs to be changed, because now it sets the IBD status.