feat: improve scraper startup error handling (#5191)

### Description

- handle errors and sets set chain metrics if scraper fails for chain
during startup

### Drive-by changes
 - implement Clone for `ScraperDb`
- this is because DbConn doesn't implement Clone when `mock` feature is
enabled

### Related issues
Fixes https://github.com/hyperlane-xyz/issues/issues/1408

### Backward compatibility

Yes

### Testing

Added unittest to test function. But don't have tests in place for
testing the logic in `Scraper::run()`

rust/main/agents/scraper/Cargo.toml

@@ -34,7 +34,12 @@ hyperlane-core = { path = "../../hyperlane-core", features = ["agent"] }
 migration = { path = "migration" }
 
 [dev-dependencies]
+reqwest.workspace = true
+sea-orm = { workspace = true, features = ["mock"]}
 tokio-test = "0.4"
+tracing-test.workspace = true
+ethers-prometheus = { path = "../../ethers-prometheus", features = ["serde"] }
+hyperlane-ethereum = { path = "../../chains/hyperlane-ethereum" }
 hyperlane-test = { path = "../../hyperlane-test" }
 
 [features]