move fetch metadata to a separate crate subxt_utils_fetchmetadata

[niklasad1]

Close #1812

This PR moves the fetch metadata to a separate crate and also makes it optional for the subxt macro/codegen use it behind a feature flag.

So, if one disables jsonrpsee in subxt then the following would end-up in a compile error:

#[subxt(runtime_metadata_insecure_url = "ws://localhost:9944")]
mod runtime {}

fn main() {}

error: 'runtime_metadata_insecure_url' requires the 'runtime-metadata-insecure-url' feature to be enabled
  --> src/main.rs:75:1
   |
75 | #[subxt::subxt(runtime_metadata_insecure_url = "ws://localhost:9944")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the attribute macro `subxt::subxt` (in Nightly builds, run with -Z macro-backtrace for more info)

[niklasad1]

we are using cargo-machete anyway for unused deps and I don't want to add

#[cfg(all(feature = "jsonrpsee", not(feature = "fetch-metadata))] use {tokio as _, url as _}

[jsdw]

I guess this means that, without importing jsonrpsee myself to enable TLS features, that we won't be able to use fetch-metadata with httpS urls?

[niklasad1]

yes without jsonrpsee it will only work to fetch metadata from a file or runtime path...

[jsdw]

Sorry, I meant that based on these feature changes, jsonrpsee won't work with TLS urls now unless I import it in my top level package to enable them or something like that!

[niklasad1]

ooooh, tls enabled by default by the ws-client and http-client :P

[jsdw]

Nit: Just to align with the above I'd call it runtime-url orrr, rename both to match the attrs so we have:

runtime-metadata-path
runtime-metadata-insecure-url

[jsdw]

Looks good; A step in the right direction I think!

I'm still on the fence over having one utils crate versus several (because feature flags make everything messier) but this is a step up from the current state :)

[lexnv]

Nice! Had a brief view over the PR and looks solid 👍