substrate-prometheus-endpoint: directly require the feature "tokio/net" (#9355)

The crate `substrate-prometheus-endpoint` use tokio items given by the
feature "net" but it doesn't explictly requires it in the `Cargo.toml`.
It compiles on master because `hyper-util` enables the feature
"tokio/net". But upgrading `hyper-util` break this indirect enabling.

This fix the issue by directly setting "net" feature as required, as it
is used.
We should also backport this ideally. It is not a breaking change given
the code doesn't compile without the feature and only compiles if
indirectly enabled by another crate.

# Reproduce:

To reproduce do `cargo update -p hyper-util && cargo check -p
substrate-prometheus-endpoint`:

You will get the error:
```
error[E0433]: failed to resolve: could not find `TcpListener` in `net`
  --> substrate/utils/prometheus/src/lib.rs:89:29
   |
89 |     let listener = tokio::net::TcpListener::bind(&prometheus_addr).await.map_err(|e| {
   |                                ^^^^^^^^^^^ could not find `TcpListener` in `net`
   |
note: found an item that was configured out
  --> /home/gui/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.45.0/src/net/mod.rs:43:28
   |
43 |     pub use tcp::listener::TcpListener;
   |                            ^^^^^^^^^^^
note: the item is gated behind the `net` feature
  --> /home/gui/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.45.0/src/net/mod.rs:38:1
   |
38 | / cfg_net! {
39 | |     mod lookup_host;
40 | |     pub use lookup_host::lookup_host;
...  |
51 | |     }
52 | | }
   | |_^
   = note: this error originates in the macro `cfg_net` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider importing this struct
   |
20 + use std::net::TcpListener;
   |
help: if you import `TcpListener`, refer to it directly
   |
89 -     let listener = tokio::net::TcpListener::bind(&prometheus_addr).await.map_err(|e| {
89 +     let listener = TcpListener::bind(&prometheus_addr).await.map_err(|e| {
   |

error[E0412]: cannot find type `TcpListener` in module `tokio::net`
  --> substrate/utils/prometheus/src/lib.rs:99:24
   |
99 |     listener: tokio::net::TcpListener,
   |                           ^^^^^^^^^^^ not found in `tokio::net`
   |
note: found an item that was configured out
  --> /home/gui/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.45.0/src/net/mod.rs:43:28
   |
43 |     pub use tcp::listener::TcpListener;
   |                            ^^^^^^^^^^^
note: the item is gated behind the `net` feature
  --> /home/gui/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tokio-1.45.0/src/net/mod.rs:38:1
   |
38 | / cfg_net! {
39 | |     mod lookup_host;
40 | |     pub use lookup_host::lookup_host;
...  |
51 | |     }
52 | | }
   | |_^
   = note: this error originates in the macro `cfg_net` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider importing this struct
   |
20 + use std::net::TcpListener;
   |
help: if you import `TcpListener`, refer to it directly
   |
99 -     listener: tokio::net::TcpListener,
99 +     listener: TcpListener,
   |

Some errors have detailed explanations: E0412, E0433.
For more information about an error, try `rustc --explain E0412`.
error: could not compile `substrate-prometheus-endpoint` (lib) due to 2 previous errors
```

---------

Co-authored-by: cmd[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Bastian Köcher <[email protected]>
(cherry picked from commit fb451c7)

Author: 3 people

prdoc/pr_9355.prdoc

@@ -0,0 +1,11 @@
+title: 'substrate-prometheus-endpoint: directly require the feature "tokio/net"'
+doc:
+- audience: Node Dev
+  description: |-
+    The crate `substrate-prometheus-endpoint` use tokio items given by the feature "net" but it doesn't explictly requires it in the `Cargo.toml`. It compiles on master because `hyper-util` enables the feature "tokio/net". But upgrading `hyper-util` break this indirect enabling.
+
+    This fix the issue by directly setting "net" feature as required, as it is used.
+    We should also backport this ideally. It is not a breaking change given the code doesn't compile without the feature and only compiles if indirectly enabled by another crate.
+crates:
+- name: substrate-prometheus-endpoint
+  bump: patch

substrate/utils/prometheus/Cargo.toml

@@ -22,7 +22,7 @@ hyper-util = { features = ["server-auto", "server-graceful", "tokio"], workspace
 log = { workspace = true, default-features = true }
 prometheus = { workspace = true }
 thiserror = { workspace = true }
-tokio = { features = ["parking_lot"], workspace = true, default-features = true }
+tokio = { features = ["net", "parking_lot"], workspace = true, default-features = true }
 
 [dev-dependencies]
 hyper-util = { features = ["client-legacy", "tokio"], workspace = true, default-features = true }