fix(parser): remove dead precedence declarations [#215 family F]

Menhir emitted 16 "precedence level / %prec ... never useful"
warnings — declarations that never resolve any conflict because the
expression cascade disambiguates structurally. They are pure noise
that, alongside the conflict warnings, make a healthy build look
broken.

Removed (all certified "never useful" by Menhir itself):

  - precedence level: `%right EQ PLUSEQ MINUSEQ STAREQ SLASHEQ`
    (assignment ops — handled at statement level, never in the
    expr operator cascade)
  - precedence level: `%right BANG TILDE UMINUS UREF UDEREF`
    (unary level — `expr_unary` is right-recursive and already
    unambiguous)
  - precedence level: `%left DOT LBRACKET LPAREN`
    (postfix level — `expr_postfix` disambiguates structurally)
  - the three now-orphaned `%prec UMINUS/UREF/UDEREF` on the unary
    rules (UMINUS/UREF/UDEREF were pseudo-tokens used only there)

Provably parse-behaviour-neutral — removing a declaration Menhir
certifies resolves nothing cannot change any resolution. Verified:

  - 16 "never useful" warnings: gone (0 remain)
  - conflict counts UNCHANGED: 72 S/R, 10 R/R, 23 S/R states,
    4 R/R states (identical resolution profile)
  - `dune test --force` green at 257/257

The retained `LOWEST_TYPE_ARROW`/`ARROW` levels (#216, family A) are
*not* flagged — they do real work.

Refs #215

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

lib/parser.mly

@@ -97,7 +97,6 @@ let rec effect_union_of_list = function
    See affinescript#215 (family A). */
 %nonassoc LOWEST_TYPE_ARROW
 %nonassoc ARROW
-%right EQ PLUSEQ MINUSEQ STAREQ SLASHEQ
 %left PIPEPIPE
 %left AMPAMP
 %left PIPE
@@ -108,8 +107,15 @@ let rec effect_union_of_list = function
 %left LTLT GTGT
 %left PLUS PLUSPLUS MINUS
 %left STAR SLASH PERCENT
-%right BANG TILDE UMINUS UREF UDEREF
-%left DOT LBRACKET LPAREN
+/* Removed (affinescript#215 family F): the assignment-op level
+   (EQ PLUSEQ MINUSEQ STAREQ SLASHEQ), the unary level
+   (BANG TILDE UMINUS UREF UDEREF), and the postfix level
+   (DOT LBRACKET LPAREN) — Menhir certified every one of these
+   precedence levels "never useful" (they resolve no conflict; the
+   expr cascade disambiguates structurally). Removal is
+   parse-behaviour-neutral, proven by the unchanged conflict counts
+   and the green 257-test gate. UMINUS/UREF/UDEREF were pseudo-tokens
+   used only by the now-removed `%prec` on the unary rules. */
 
 /* Entry point */
 %start <Ast.program> program
@@ -707,11 +713,11 @@ expr_mul:
   | e = expr_unary { e }
 
 expr_unary:
-  | MINUS e = expr_unary %prec UMINUS { ExprUnary (OpNeg, e) }
+  | MINUS e = expr_unary { ExprUnary (OpNeg, e) }
   | BANG e = expr_unary { ExprUnary (OpNot, e) }
   | TILDE e = expr_unary { ExprUnary (OpBitNot, e) }
-  | AMP e = expr_unary %prec UREF { ExprUnary (OpRef, e) }
-  | STAR e = expr_unary %prec UDEREF { ExprUnary (OpDeref, e) }
+  | AMP e = expr_unary { ExprUnary (OpRef, e) }
+  | STAR e = expr_unary { ExprUnary (OpDeref, e) }
   | e = expr_postfix { e }
 
 expr_postfix: