Use Polygon gas oracle (#2965)

After investigating #2959, I found the following

this is a known problem with Polygon, explanation here
ethers-io/ethers.js#2828 (comment)

Fun fact Asa looked into this once
#771

Here's a discussion it in Foundry, which I found hoping that ethers-rs
folks had ran into this before
foundry-rs/foundry#1703

Foundry fixed this by using the Polygon gas station oracle which seems
to be recommended path
https://github.com/foundry-rs/foundry/pull/3368/files#diff-c89a4bbf7a90da118dcf00c5fe70eba78f8e5d95662bb5f039a353113e95042bR205

There's actually a polygon ethers middleware for this
https://docs.rs/ethers/latest/ethers/middleware/gas_oracle/polygon/struct.Polygon.html

So I (originally) borrowed this code from Foundry
https://github.com/foundry-rs/foundry/blob/master/crates/common/src/provider.rs#L254-L290

Changed to use Middlewares

This also means we can remove our existing janky Polygon logic

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