feat: add Process.pid and Process.ppid foreign static methods to os module

Implement uv_os_getpid() and uv_os_getppid() bindings in process.c, register them in the CLI module table, expose as foreign statics in os.wren, and add a test suite verifying both return positive integers with pid greater than ppid.

test/os/process/pid_and_ppid.wren

@@ -0,0 +1,11 @@
+import "os" for Process
+
+System.print(Process.pid is Num) // expect: true
+System.print(Process.pid.isInteger) // expect: true
+System.print(Process.pid > 0) // expect: true
+
+System.print(Process.ppid is Num) // expect: true
+System.print(Process.ppid.isInteger) // expect: true
+System.print(Process.ppid > 0) // expect: true
+
+System.print(Process.pid > Process.ppid) // expect: true