Update process.Pipe to return List[Byte] on read

Conform `read_bytes` on Pipe utility object to updated file descriptor
`read_bytes` api

Signed-off-by: Hristo I. Gueorguiev <53634432+izo0x90@users.noreply.github.com>

stdlib/src/os/process.mojo

@@ -18,8 +18,7 @@ Example:
 from os import Process
 ```
 """
-from collections import Optional
-from collections.string import StringSlice
+from collections import List, Optional
 
 from sys import (
     os_is_linux,
@@ -137,15 +136,15 @@ struct Pipe:
             raise Error("Can not write from read only side of pipe")
 
     @always_inline
-    fn read_bytes(mut self, size: Int) raises -> Span[Byte, MutableAnyOrigin]:
+    fn read_bytes(mut self, size: Int) raises -> List[Byte]:
         """
-        Read a span of bytes from this pipe.
+        Read a number of bytes from this pipe.
 
         Args:
             size: The number of bytes to read from this pipe.
 
         Returns:
-            Span of bytes with len=size read from this pipe.
+            List of bytes with len=size read from this pipe.
         """
         if self.fd_in:
             return self.fd_in.value().read_bytes(size)
@@ -265,7 +264,7 @@ struct Process:
                 raise Error("Unable to fork parent")
 
             pipe.set_input_only()
-            var err: Optional[Span[Byte, MutableAnyOrigin]]
+            var err: Optional[List[Byte]]
             try:
                 err = pipe.read_bytes(exec_err_code.byte_length())
             except e:
@@ -274,7 +273,7 @@ struct Process:
             if (
                 err
                 and len(err.value()) > 0
-                and StringSlice(unsafe_from_utf8=err.value()) == exec_err_code
+                and err.value().__str__() == exec_err_code
             ):
                 raise Error("Failed to execute " + path)