Merge #9: fix: set TcpListener to non-blocking mode before passing to axum-server

8cdb2d9 fix: set TcpListener to non-blocking mode before passing to axum-server (Jose Celano)

Pull request description:

  ## Description

  This PR fixes the Tokio runtime panic that occurs when running the application with `cargo run`.

  ## Problem

  The application was panicking with:
  ```
  Registering a blocking socket with the tokio runtime is unsupported. If you wish to do anyways, please add `--cfg tokio_allow_from_blocking_fd` to your RUSTFLAGS.
  ```

  ## Root Cause

  - Tokio 1.44.0 introduced stricter validation to prevent blocking file descriptors from being registered with the async runtime
  - `std::net::TcpListener::bind()` creates blocking sockets by default
  - axum-server 0.8.0 internally uses `tokio::net::TcpListener::from_std()` which panics when it detects a blocking socket

  ## Solution

  Set the `TcpListener` to non-blocking mode **before** passing it to axum-server by calling `socket.set_nonblocking(true)` immediately after binding.

  ## Changes

  - ✅ Added `socket.set_nonblocking(true)` in `src/api/mod.rs` after binding the TcpListener
  - ✅ Removed the incorrect RUSTFLAGS workaround from README.md troubleshooting section
  - ✅ Deleted temporary TOKIO_BLOCKING_SOCKET_FIX.md file

  ## Benefits

  - Proper fix instead of masking the symptom with RUSTFLAGS
  - Prevents potential performance issues under load
  - Application now runs correctly with just `cargo run`

  ## Testing

  Verified that the application starts successfully without any panic:
  ```bash
  cargo run
  ```

  Fixes #8

  ## References

  - [Tokio Issue #7172](tokio-rs/tokio#7172)
  - [Tokio PR #7166](tokio-rs/tokio#7166)

ACKs for top commit:
  josecelano:
    ACK 8cdb2d9

Tree-SHA512: 12653e0a924f03fb6e43d9eb381aec6e593227f2a095ba681b952c3851ed09575a2a5cbca2b0fd6d0647d9c777d4a28418bc51e768568f618457614c34b02b15

Author: josecelano

README.md

@@ -45,22 +45,6 @@ You can check the API with the health_check endpoint: <http://127.0.0.1:3000/hea
 
 ## Troubleshooting
 
-### Tokio Runtime Error
-
-If you encounter an error like:
-
-```text
-Registering a blocking socket with the tokio runtime is unsupported. If you wish to do anyways, please add `--cfg tokio_allow_from_blocking_fd` to your RUSTFLAGS.
-```
-
-You need to set the RUSTFLAGS environment variable when building and running the application:
-
-```console
-RUSTFLAGS="--cfg tokio_allow_from_blocking_fd" cargo run
-```
-
-This is a known issue with the tokio runtime on certain systems. The flag allows the application to register blocking file descriptors with the async runtime.
-
 ### Session Directory Not Found
 
 If you see an error about the session output directory not being found:

src/api/mod.rs

@@ -34,6 +34,10 @@ pub async fn start(bind_to: &SocketAddr, state: AppState) {
     let socket =
         std::net::TcpListener::bind(bind_to).expect("Could not bind tcp_listener to address.");
 
+    socket
+        .set_nonblocking(true)
+        .expect("Failed to set socket to non-blocking mode");
+
     let server_address = socket
         .local_addr()
         .expect("Could not get local_addr from tcp_listener.");