Inline readable-web-to-node-stream into @web5/agent

[shamilovtim]

@web5/agent is the only package in our dependency tree that uses readable-web-to-node-stream which is one file, 39 lines of code and hasn't been updated in 3 years. We use it in only one place in @web5/agent. We can remove this package from our supply chain with one file. In addition, readable-web-to-node-stream has source map errors and relies on old versions of dependencies.