fst: implement app id parser

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

fst/shared.go

@@ -1,18 +1,2 @@
 // Package fst exports shared fortify types.
 package fst
-
-import (
-	"crypto/rand"
-	"encoding/hex"
-)
-
-type ID [16]byte
-
-func (a *ID) String() string {
-	return hex.EncodeToString(a[:])
-}
-
-func NewAppID(id *ID) error {
-	_, err := rand.Read(id[:])
-	return err
-}