Scraper: H512 tx hashes for eventual Solana support

[tkporter]

Note:

This isn't strictly required at the moment, and is only strictly needed for the scraper to work well with Solana chains for when we eventually implement this!

Problem

Because of Solana's 64 byte tx hash lengths (instead of the typical 32 bytes in Ethereum), we moved much of the agent code to using H512 for tx hashes. However we didn't change the scraper - it still works only with 32 byte tx hashes.

We'll still use bytea which isn't fixed length for storing tx hashes. However we'll need to change some logic to support H512 tx hashes to avoid stuff like this:

hyperlane-monorepo/rust/agents/scraper/src/chain_scraper/mod.rs

Line 84 in 02d5549

.expect("256-bit transaction ids are the maximum supported at this time"),

Solution

Our options are:

1. always write H512s, and have application logic know to grab the latter 32 bytes for Ethereum chains, etc
2. write tx hashes with a length dependent upon the protocol being used

1 is probably easier in the way that things are set up in the agent codebase