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

[josecelano]

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:

cargo run

Fixes #8

References

• Tokio Issue #7172
• Tokio PR #7166

[josecelano]

ACK 8cdb2d9