replace non-specific dependencies

**Is your feature request related to a problem? Please describe.**

We import the entire `alloy` & `reth(-optimism-node)` crates but we really only need a few things, accessible via sub-crates (e.g. [alloy-transport-http](https://github.com/alloy-rs/alloy/tree/main/crates/transport-http)). We could shave down build times by replacing these crates with sub-crates where possible. I'm not sure how much we can do with reth deps (hopefully we can, we only use its types), but I know alloy deps could be shaved down.

**Describe the solution you'd like**

- figure out which crates can be replaced with more-specific sub-crates (check the root [Cargo.toml](https://github.com/flashbots/contender/blob/main/Cargo.toml))
- replace them
- focus on `reth` and `alloy` but if you find any others, feel free to add them