fix: set TcpListener to non-blocking before registering with Tokio

[qianxiaoming]

Description
This PR fixes a runtime panic when running the example report server.

Reproduction
Environment:
• Rust 1.94.0
• macOS 26.4

Command:

cargo run -- check examples/datasets/simple_points.geojson

Output:

[INFO ] Discovered 15 rules
[INFO ] Check complete: 0 findings from 15 rules
[INFO ] Report server running at http://127.0.0.1:53100
[INFO ] Opening report at http://127.0.0.1:53100

thread 'main' (516969) panicked at src/report/visual/server.rs:77:20:
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. See github.com/tokio-rs/tokio/issues/7172 for details.
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

Fix
Set the TcpListener to non-blocking before registering it with Tokio:

listener.set_nonblocking(true)?;

This prevents the panic and allows the report server to run correctly.