rename host references in BlockWatcher to rollup

[Evalir]

Summary

Renames "host" terminology to "rollup" in BlockWatcher to accurately reflect what it watches. The watcher subscribes to blocks on the rollup chain, not the host chain, so the prior naming was misleading.

Changes

• Module/struct doc comments updated from "Host chain" → "Rollup chain"
• host_provider field and constructor parameters renamed to rollup_provider
• Log messages ("subscribed to host chain blocks", "updated host block number") updated to say "rollup"

Breaking change

BlockWatcher::new and BlockWatcher::with_current_block parameter names changed. Callers using positional args are unaffected; any callers passing the argument by name will need to update.

Test plan

• cargo clippy -p init4-bin-base --all-features --all-targets passes

[Evalir]

• rename host references in BlockWatcher to rollup #141 👈 (View in Graphite)
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[Fraser999]

I wonder if we should just remove all mention of "host" or "rollup" since the block watcher could be used to track either chain?

[Evalir]

i'm amenable to that, it's probably the best choice