Refactor cfold propagation and add eager mode

Refactor `cfold` in `ecPhlCodeTx` to track propagated substitutions
and preserved dependencies explicitly, and use that state to decide
when folding can continue across assignments and structured
instructions.

Add an eager `cfold*` variant that keeps folding by promoting
preserved variables into the propagated substitution when possible,
and extend `tests/cfold.ec` with coverage for both the default and
eager behaviors.

Author: Gustavo2622

src/ecPV.ml

@@ -47,6 +47,7 @@ module PVMap = struct
     Mnpv.find_opt (pvm m.pvm_env k) m.pvm_map
 
   let raw m = m.pvm_map
+
 end
 
 (* -------------------------------------------------------------------- *)

src/ecParser.mly

@@ -2991,7 +2991,10 @@ interleave_info:
     { Pinterleave info }
 
 | CFOLD s=side? c=codepos n=word?
-    { Pcfold (s, c, n) }
+    { Pcfold (s, c, n, false) }
+
+| CFOLD STAR s=side? c=codepos n=word?
+    { Pcfold (s, c, n, true) }
 
 | RND s=side? info=rnd_info c=prefix(COLON, semrndpos)?
     { Prnd (s, c, info) }

src/ecParsetree.ml

@@ -757,7 +757,7 @@ type phltactic =
   | Pcond          of pcond_info
   | Pmatch         of matchmode
   | Pswap          of ((oside * pswap_kind) located list)
-  | Pcfold         of (oside * pcodepos * int option)
+  | Pcfold         of (oside * pcodepos * int option * bool) (* side + 1st inst + n lines + eager? *)
   | Pinline        of inline_info
   | Poutline       of outline_info
   | Pinterleave    of interleave_info located