system: enforce absolute paths

This is less error-prone, and is quite easy to integrate considering internal/app has already migrated to container.Absolute.

Closes #11.

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

system/tmpfiles.go

@@ -8,14 +8,15 @@ import (
 	"os"
 	"syscall"
 
+	"hakurei.app/container"
 	"hakurei.app/hst"
 )
 
 // CopyFile reads up to n bytes from src and writes the resulting byte slice to payloadP.
-func (sys *I) CopyFile(payloadP *[]byte, src string, cap int, n int64) *I {
+func (sys *I) CopyFile(payloadP *[]byte, src *container.Absolute, cap int, n int64) *I {
 	buf := new(bytes.Buffer)
 	buf.Grow(cap)
-	sys.ops = append(sys.ops, &tmpfileOp{payloadP, src, n, buf})
+	sys.ops = append(sys.ops, &tmpfileOp{payloadP, src.String(), n, buf})
 	return sys
 }