fix: replace with erc6492 lib and call rpc directly w/o http

[chris13524]

Description

Removes the dependency on WalletConnectRust and uses the erc6492 library directly. Also upgrades to use a "self provider" pattern where the EVM library directly calls into the RPC proxy function rather than using HTTP.

Two other things:

• Updates the just Rust version to be stable, rather than nightly, as there were some new clippy errors in nightly that weren't showing in CI
• Adds Content-Type header to README as this is technically the spec of JSON-RPC, even though Blockchain API doesn't require it. This confused me when I attempted to run the same commands against a regular RPC endpoint but got a bad request because I didn't supply this header.

Remaining work:

• [ ] Iron out error handling in self_transport.rs

How Has This Been Tested?

Not tested?

Due Diligence

• [ ] Breaking change
• [ ] Requires a documentation update
• [ ] Requires a e2e/integration test update