Add example for using `EsploraClient` with timeout configuration

[ChidiChuks]

Feature Request

An example showing how to configure and use EsploraClient with custom timeout settings would be helpful for developers using BDK with unreliable or slow network connections.

Why?

Currently, the documentation does not illustrate how to:

• Set custom request timeouts when using EsploraClient
• Handle timeout-related errors gracefully

What’s Expected?

Please add a simple example (in the examples/ directory) demonstrating:

• Instantiating EsploraClient with a custom ureq::Agent
• Setting timeout durations (connect/read/write)
• Making a sample call (e.g., get_height or get_tx) with the client

Example Reference

The relevant code might look like:

let agent = ureq::AgentBuilder::new()
    .timeout_connect(Duration::from_secs(10))
    .timeout_read(Duration::from_secs(30))
    .timeout_write(Duration::from_secs(30))
    .build();

let esplora_client = EsploraClient::from_agent("https://blockstream.info/api", agent);