fix: expose pcid handoff to spawned drivers

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

local/patches/base/P4-pcid-public-client-channel.patch

@@ -0,0 +1,8 @@
+--- a/drivers/pcid/src/driver_interface/mod.rs
++++ b/drivers/pcid/src/driver_interface/mod.rs
+@@ -310,4 +310,4 @@ impl PciFunctionHandle {
+-    fn connect_default() -> Self {
++    pub fn connect_default() -> Self {
+         let channel_fd = match env::var("PCID_CLIENT_CHANNEL") {
+             Ok(channel_fd) => channel_fd,
+             Err(err) => {