Bambu TLS trust config + finish PrusaLink/PrusaSerial split

Certs:
- Vendor Bambu's shared LAN-mode root CA (certs/bambu_ca2.pem, verified
  self-signed CA:TRUE, see certs/README.md for provenance/fingerprint).
- Config gains bambu_ca_cert_path (per-printer override) and
  bambu_require_valid_cert (the allow/reject flag); printer::bambu::BambuTls
  turns those into BundledCa/Custom/Insecure. connect() doesn't perform a
  real handshake yet (no TLS-capable MQTT client wired in), just reports
  which trust mode it would use.

Also reconciles a rename in flight (Printer -> GenericPrinter trait) and
finishes the PrusaPrinter -> PrusaLinkPrinter/PrusaSerialPrinter split:
added the missing GenericPrinter impl for PrusaSerialPrinter, fixed
PrinterHandle's variant payload types, updated mod.rs's pub use list and
doc comments, and updated the example to the new 5-variant shape.

Verified with cargo check --all-targets (0 errors) and a full run of
cargo run --example printer_polymorphism.

src/printer/mod.rs

@@ -1,5 +1,5 @@
 //! Printer hierarchy — the Rust answer to
-//! `GenericPrinter -> BambuPrinter/PrusaPrinter/KlipperPrinter`-style
+//! `GenericPrinter -> BambuV1/BambuV2/PrusaLink/PrusaSerial/Klipper`-style
 //! inheritance, since Rust structs can't `extend` each other.
 //!
 //! Three pieces, each doing one job an OOP base class would normally do:
@@ -7,10 +7,10 @@
 //! 1. `PrinterBase` — a plain struct holding the shared *fields*. Every
 //!    printer struct below *has* one of these (composition) instead of
 //!    *extending* one.
-//! 2. `Printer` — a trait holding the shared *behavior*. `connect()` has no
-//!    default body, so every printer type is forced to write its own —
-//!    that's what "overriding" looks like when there's no inherited body to
-//!    override in the first place.
+//! 2. `GenericPrinter` — a trait holding the shared *behavior*. `connect()`
+//!    has no default body, so every printer type is forced to write its
+//!    own — that's what "overriding" looks like when there's no inherited
+//!    body to override in the first place.
 //! 3. `PrinterHandle` — an enum listing the closed set of printer kinds.
 //!    Stands in for "any subclass of GenericPrinter".
 //!
@@ -25,9 +25,9 @@ mod bambu;
 mod klipper;
 mod prusa;
 
-pub use bambu::BambuPrinter;
+pub use bambu::{BambuPrinter, BambuTls};
 pub use klipper::KlipperPrinter;
-pub use prusa::PrusaPrinter;
+pub use prusa::{PrusaLinkPrinter, PrusaSerialPrinter};
 
 /// A tiny error type: just a message. `String` would work too — this exists
 /// mainly so `?` has something concrete to convert into everywhere.
@@ -43,9 +43,9 @@ pub struct PrinterBase {
     pub host: String,
 }
 
-/// The shared interface — think `interface Printer` (Java/TS) or an ABC
-/// (Python). Every vendor's struct implements this.
-pub trait Printer {
+/// The shared interface — think `interface GenericPrinter` (Java/TS) or an
+/// ABC (Python). Every vendor's struct implements this.
+pub trait GenericPrinter {
     /// Read-only access to the shared fields.
     fn base(&self) -> &PrinterBase;
 
@@ -69,10 +69,20 @@ pub trait Printer {
     }
 }
 
+pub enum PrinterFlavour {
+    BambuV1Printer,
+    BambuV2Printer,
+    PrusaLinkPrinter,
+    PrusaSerialPrinter,
+    KlipperPrinter,
+}
+
 /// The closed set of printer kinds this fleet can talk to.
 pub enum PrinterHandle {
-    Bambu(BambuPrinter),
-    Prusa(PrusaPrinter),
+    BambuV1(BambuPrinter),
+    BambuV2(BambuPrinter),
+    PrusaLink(PrusaLinkPrinter),
+    PrusaSerial(PrusaSerialPrinter),
     Klipper(KlipperPrinter),
 }
 
@@ -80,19 +90,23 @@ pub enum PrinterHandle {
 // and forwards to that variant's own implementation. This one block is the
 // only "boilerplate tax" for not having inheritance — everything else reads
 // like normal code.
-impl Printer for PrinterHandle {
+impl GenericPrinter for PrinterHandle {
     fn base(&self) -> &PrinterBase {
         match self {
-            PrinterHandle::Bambu(p) => p.base(),
-            PrinterHandle::Prusa(p) => p.base(),
+            PrinterHandle::BambuV1(p) => p.base(),
+            PrinterHandle::BambuV2(p) => p.base(),
+            PrinterHandle::PrusaLink(p) => p.base(),
+            PrinterHandle::PrusaSerial(p) => p.base(),
             PrinterHandle::Klipper(p) => p.base(),
         }
     }
 
     async fn connect(&mut self) -> Result<(), PrinterError> {
         match self {
-            PrinterHandle::Bambu(p) => p.connect().await,
-            PrinterHandle::Prusa(p) => p.connect().await,
+            PrinterHandle::BambuV1(p) => p.connect().await,
+            PrinterHandle::BambuV2(p) => p.connect().await,
+            PrinterHandle::PrusaLink(p) => p.connect().await,
+            PrinterHandle::PrusaSerial(p) => p.connect().await,
             PrinterHandle::Klipper(p) => p.connect().await,
         }
     }