internal/pipewire: move Core wrapper methods under Core

These do not belong under Context, and is an early implementation limitation that carried over.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pipewire/pipewire.go

@@ -122,7 +122,7 @@ func New(conn Conn, props SPADict) (*Context, error) {
 	}
 	ctx.nextId = Int(len(ctx.proxy))
 
-	if err := ctx.coreHello(); err != nil {
+	if err := ctx.core.hello(); err != nil {
 		return nil, err
 	}
 	if err := ctx.clientUpdateProperties(props); err != nil {