feat: add embassy-usb 0.6 server support

Add `embassy-usb-0_6-server` feature flag enabling use of embassy-usb
v0.6.0 alongside the existing v0.5 support. The new server module
mirrors the v0.5 implementation, updated for embassy-sync 0.8 (required
by embassy-usb 0.6). embassy-usb-driver remains at 0.2 (unchanged).

Both `embassy-usb-0_5-server` and `embassy-usb-0_6-server` can be
enabled simultaneously for projects in transition.

New dependencies (all optional):
- embassy-usb 0.6
- embassy-sync 0.8

Author: Felipe Balbi

source/postcard-rpc/Cargo.toml

@@ -19,6 +19,7 @@ features = [
     "cobs-serial",
     "raw-nusb",
     "embassy-usb-0_5-server",
+    "embassy-usb-0_6-server",
     "embedded-io-async-0_6-server",
     "_docs-fix",
     # TODO: What to do about the webusb feature? Can we do separate target builds?
@@ -117,6 +118,11 @@ package = "embassy-usb"
 version = "0.5"
 optional = true
 
+[dependencies.embassy-usb-0_6]
+package = "embassy-usb"
+version = "0.6"
+optional = true
+
 [dependencies.embassy-usb-driver-0_2]
 package = "embassy-usb-driver"
 version = "0.2"
@@ -127,6 +133,11 @@ package = "embassy-sync"
 version = "0.7"
 optional = true
 
+[dependencies.embassy-sync-0_8]
+package = "embassy-sync"
+version = "0.8"
+optional = true
+
 [dependencies.static_cell]
 version = "2.1"
 optional = true
@@ -232,6 +243,16 @@ embassy-usb-0_5-server = [
     "dep:embassy-futures",
 ]
 
+embassy-usb-0_6-server = [
+    "dep:embassy-usb-0_6",
+    "dep:embassy-sync-0_8",
+    "dep:static_cell",
+    "dep:embassy-usb-driver-0_2",
+    "dep:embassy-executor",
+    "dep:embassy-time",
+    "dep:embassy-futures",
+]
+
 embedded-io-async-0_6-server = [
     "dep:embassy-sync-0_7",
     "dep:static_cell",