Add upload_project_file/send_gcode_line, real Marlin serial, Bambu protocol auto-detect

- GenericPrinter grows upload_project_file, send_gcode_line, and a
  generic upload_gcode<P> driver that streams a whole gcode file line by
  line through any vendor's send_gcode_line.
- PrusaSerialPrinter's connect/send_gcode_line are real (not stubs): a
  held-open MarlinSerialConnection (src/printer/marlin_serial.rs) writes
  each line and waits for Marlin's "ok" before sending the next. Config
  changed from com_port: i16 to port: String + baud_rate: u32 to hold a
  real device path.
- Bambu: BambuGenericPrinter + BambuV1Printer/BambuV2Printer collapsed
  into one BambuPrinter, since which MQTT/BambuMQTT version (v3.1.1/v1
  vs v5/v2) a printer speaks is discovered at connect() time (or forced),
  not something config should pick a type for - the same physical
  printer can change after a firmware update. printers.toml gets a new
  "bambu" vendor (auto-detect, the default) alongside bambu_v1/bambu_v2
  (force a specific one).
- Bambu's gcode_line request is now built for real via
  continuum-schema-instance against continuum-schemas' JSON Schema,
  picking the v1 or v2 schema directory based on the detected protocol
  version, instead of a hand-written serde struct.
- Added rumqttc as a dependency (not wired up yet - the real MQTT
  v5-then-v3.1.1 fallback connect and the publish/receive plumbing are
  still stubs).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MWQVtBGxHYLkVw2kBupd5g

Cargo.toml

@@ -34,6 +34,18 @@ name = "bambu_commands_demo"
 path = "examples/bambu_commands_demo.rs"
 
 [dependencies]
+# Real printer protocol clients (MQTT for Bambu, HTTP for PrusaLink/
+# Moonraker, FTPS for gcode transfer) go here once you're ready to build
+# past the stubs in src/printer/ - see that module's doc comment.
+continuum-rust-types = { path = "../continuum-schemas/packages/rust-types" }
+# FOR NON-LOCAL DEV
+# continuum-rust-types = { git = "https://git.octoturge.com/Continuum/continuum-schemas.git" }
+
+# Builds a JSON instance straight from the schema files in
+# continuum-schemas/schemas/ - used for Bambu's raw MQTT JSON messages
+# instead of hand-written serde structs (see bambu.rs).
+continuum-schema-instance = { path = "../continuum-common/packages/rust-schema-instance" }
+
 tokio = { version = "1.40", features = ["full"] }
 tokio-tungstenite = { version = "0.24", features = ["native-tls"] }
 futures-util = "0.3"
@@ -47,10 +59,5 @@ tracing-subscriber = { version = "0.3", features = ["env-filter", "json"] }
 anyhow = "1"
 thiserror = "1"
 dotenvy = "0.15"
-
-# Real printer protocol clients (MQTT for Bambu, HTTP for PrusaLink/
-# Moonraker, FTPS for gcode transfer) go here once you're ready to build
-# past the stubs in src/printer/ - see that module's doc comment.
-continuum-rust-types = { path = "../continuum-schemas/packages/rust-types" }
-# FOR NON-LOCAL DEV
-# continuum-rust-types = { git = "https://git.octoturge.com/Continuum/continuum-schemas.git" }
+tokio-serial = { version = "5.5.0", default-features = false }
+rumqttc = "0.25.1"