feat(plugins): add SubsonicAPI CallRaw, with support for raw=true binary response for host functions (#4982)

* feat: implement raw binary framing for host function responses

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: add CallRaw method for Subsonic API to handle binary responses

Signed-off-by: Deluan <deluan@navidrome.org>

* test: add tests for raw=true methods and binary framing generation

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: improve error message for malformed raw responses to indicate incomplete header

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: add wasm_import_module attribute for raw methods and improve content-type handling

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

plugins/testdata/test-subsonicapi-plugin/main.go

@@ -3,6 +3,8 @@
 package main
 
 import (
+	"fmt"
+
 	"github.com/navidrome/navidrome/plugins/pdk/go/host"
 	"github.com/navidrome/navidrome/plugins/pdk/go/pdk"
 )
@@ -28,4 +30,28 @@ func callSubsonicAPIExport() int32 {
 	return 0
 }
 
+// call_subsonic_api_raw is the exported function that tests the SubsonicAPI CallRaw host function.
+// Input: URI string (e.g., "/getCoverArt?u=testuser&id=al-1")
+// Output: JSON with contentType, size, and first bytes of the raw response
+//
+//go:wasmexport call_subsonic_api_raw
+func callSubsonicAPIRawExport() int32 {
+	uri := pdk.InputString()
+
+	contentType, data, err := host.SubsonicAPICallRaw(uri)
+	if err != nil {
+		pdk.SetErrorString("failed to call SubsonicAPI raw: " + err.Error())
+		return 1
+	}
+
+	// Return metadata about the raw response as JSON
+	firstByte := 0
+	if len(data) > 0 {
+		firstByte = int(data[0])
+	}
+	result := fmt.Sprintf(`{"contentType":%q,"size":%d,"firstByte":%d}`, contentType, len(data), firstByte)
+	pdk.OutputString(result)
+	return 0
+}
+
 func main() {}