service/pam: move pam execution to subprocess to allow killing it

Many pam modules can't be aborted well without this.

src/services/pam/subprocess.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <iostream>
+
+#include <security/pam_appl.h>
+
+#include "ipc.hpp"
+
+// endls are intentional as it makes debugging much easier when the buffer actually flushes.
+// NOLINTBEGIN
+#define logIf(log)                                                                                 \
+	if (log) std::cout << "quickshell.service.pam.subprocess: "
+// NOLINTEND
+
+class PamSubprocess {
+public:
+	explicit PamSubprocess(bool log, int fdIn, int fdOut): log(log), pipes(fdIn, fdOut) {}
+	PamIpcExitCode exec(const char* configDir, const char* config, const char* user);
+	void sendCode(PamIpcExitCode code);
+
+private:
+	static int conversation(
+	    int msgCount,
+	    const pam_message** msgArray,
+	    pam_response** responseArray,
+	    void* appdata
+	);
+
+	bool log;
+	PamIpcPipes pipes;
+};