Epic: Refactor Agent Indexing: better indexing positioning, relayer fast-delivery

[tkporter]

Follows https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/3281, which is intended to be done ASAP

We should do these next - these are also in chronological order. These are less pressing but after this we'll be in a good indexing situation where we can use alternative modalities and can spin up a relayer that delivers messages without it having indexed all historical data.

### Better indexing positioning
- [ ] https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/3269
- [ ] https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/3265
- [ ] https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/3336
- [ ] https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/3266
- [ ] https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/3365
- [ ] https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/3268
- [ ] Write a quick devrel blog post on fast relayer startup without needing historing indexing

related: https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/2313 & other indexing issues https://github.com/hyperlane-xyz/hyperlane-monorepo/issues?q=is%3Aissue+is%3Aopen+indexing