IC: final implementation steps (#16801)

* removed dead code
* we need even more laziness for the generic caches
* make it bootstrap on older Nims
* wrote more deserialization code
* IC: replay required methods information

compiler/ic/packed_ast.nim

@@ -74,11 +74,9 @@ type
     flags*: TTypeFlags
     types*: seq[PackedItemId]
     n*: NodeId
-    methods*: seq[(int, PackedItemId)]
     #nodeflags*: TNodeFlags
     sym*: PackedItemId
     owner*: PackedItemId
-    attachedOps*: array[TTypeAttachedOp, PackedItemId]
     size*: BiggestInt
     align*: int16
     paddingAtEnd*: int16
@@ -111,6 +109,10 @@ type
     floats*: BiTable[BiggestFloat]
     #config*: ConfigRef
 
+  PackedInstantiation* = object
+    key*, sym*: PackedItemId
+    concreteTypes*: seq[PackedItemId]
+
 proc `==`*(a, b: SymId): bool {.borrow.}
 proc hash*(a: SymId): Hash {.borrow.}