Add a read-only dry run of a print's filament mapping

bambu_mapping_check downloads one project from the card and prints the AMS
mapping the production path would send, starting nothing.

examples/bambu_mapping_check.rs

@@ -0,0 +1,55 @@
+//! Run with: cargo run --example bambu_mapping_check -- <printer-id> <file-on-card>
+//!
+//! **Read-only dry run of what a print would do.** Connects, reads the
+//! printer's state and loaded filament, downloads one project from the SD
+//! card root over FTPS, and prints the AMS mapping the production path would
+//! send - without sending it. Starts nothing, uploads nothing, deletes
+//! nothing. An optional third argument saves the downloaded copy locally.
+
+use std::time::Duration;
+
+use continuum_proxy::fleet;
+use continuum_proxy::printer::{GenericPrinter, PrinterHandle};
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    let mut args = std::env::args().skip(1);
+    let (Some(target), Some(file)) = (args.next(), args.next()) else {
+        anyhow::bail!("usage: cargo run --example bambu_mapping_check -- <printer-id> <file-on-card> [save-to]");
+    };
+    let save_to = args.next();
+
+    let mut printers = fleet::load(std::path::Path::new("printers.toml"))?;
+    let printer = printers
+        .iter_mut()
+        .find(|p| p.base().id == target)
+        .ok_or_else(|| anyhow::anyhow!("no printer with id '{target}' in printers.toml"))?;
+    let PrinterHandle::Bambu(bambu) = printer else {
+        anyhow::bail!("'{target}' is not a Bambu printer");
+    };
+
+    tokio::time::timeout(Duration::from_secs(20), bambu.connect())
+        .await
+        .map_err(|_| anyhow::anyhow!("connect timed out"))??;
+    bambu.pushall().await.ok();
+    tokio::time::sleep(Duration::from_secs(4)).await;
+
+    let report = bambu.print_status().await.ok_or_else(|| anyhow::anyhow!("no status yet"))?;
+    println!("gcode_state: {:?}", report.gcode_state);
+    println!("{:#?}", report.ams);
+
+    let bytes = bambu.download_file(&format!("/{file}")).await?;
+    println!("downloaded {} bytes", bytes.len());
+    if let Some(path) = save_to {
+        std::fs::write(&path, &bytes)?;
+        println!("saved a copy to {path}");
+    }
+    for f in continuum_proxy::printer::plate_filaments(&bytes, 1)? {
+        println!("project filament {}: {} {} #{}", f.index, f.filament_type, f.tray_info_idx, f.color);
+    }
+    match bambu.filament_source_for(&bytes, 1).await {
+        Ok(source) => println!("mapping the production path would use: {source:?}"),
+        Err(err) => println!("the production path would REFUSE: {err}"),
+    }
+    Ok(())
+}