The argument parsing in zenoh-ext/examples should be improved.

[YuanYuYuan]

Describe the bug

cargo run --example z_pub_cache -- -l 'tcp/127.0.0.1:7447' produces the following errors

thread 'main' panicked at 'Mismatch between definition and access of `listen`. Could not downcast to &alloc::string::String, need to downcast to alloc::string::String
', zenoh-ext/examples/z_pub_cache.rs:86:32
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

To reproduce

As above.

System info

• OS: Arch Linux x86_64
• Kernel: 6.8.2-arch2-1