move fetch metadata to a separate crate subxt_utils_fetchmetadata (#1829)

* macros: feature-gate jsonrpsee/fetch metadata url

* make CI happy

* Update codegen/src/error.rs

* extract `fetch-metdata` to separate crate

* add missing license headers

* introduce subxt-utils crate

* add missing files

* codegen: remove unused hex crate

* fix test build

* move subxt_utils -> subxt_utils_fetchmetadata

* cargo fmt

* runtime-path -> runtime-metadata-path

* Update utils/fetch-metadata/src/lib.rs

utils/fetch-metadata/src/error.rs

@@ -0,0 +1,28 @@
+// Copyright 2019-2024 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+/// Error attempting to fetch metadata.
+#[derive(Debug, thiserror::Error)]
+#[non_exhaustive]
+pub enum Error {
+    /// Error decoding from a hex value.
+    #[error("Cannot decode hex value: {0}")]
+    DecodeError(#[from] hex::FromHexError),
+    /// Some SCALE codec error.
+    #[error("Cannot scale encode/decode value: {0}")]
+    CodecError(#[from] codec::Error),
+    /// JSON-RPC error fetching metadata.
+    #[cfg(feature = "url")]
+    #[error("Request error: {0}")]
+    RequestError(#[from] jsonrpsee::core::ClientError),
+    /// Failed IO when fetching from a file.
+    #[error("Failed IO for {0}, make sure that you are providing the correct file path for metadata: {1}")]
+    Io(String, std::io::Error),
+    /// URL scheme is not http, https, ws or wss.
+    #[error("'{0}' not supported, supported URI schemes are http, https, ws or wss.")]
+    InvalidScheme(String),
+    /// Some other error.
+    #[error("Other error: {0}")]
+    Other(String),
+}