go: parse.sx — binary operators via Pratt precedence climbing + 9 tests [consumes-pratt]

gp-parse-expr / gp-pratt-loop implement classic Pratt climbing
against go-precedence-table (entry shape from lib/guest/pratt.sx).
The kit gives us pratt-op-lookup + accessors; the climbing loop
itself stays per-language (per kit header — Lua and Prolog have
opposite conventions).

Left-associative ops raise the right-recursion min by 1; right-
associative would keep prec. All Go binary operators are left-assoc.

AST shape: a binary node is emitted as
  (ast-app (ast-var OP) [LHS RHS])
— canonical ast-app rather than a Go-specific binary node, since a
future evaluator can recognise operator-named apps without losing
information.

Coverage: equal-prec left-to-right, * tighter than +, && tighter
than ||, comparison tighter than &&, long left-assoc chains, mixed
literal+ident operands.

parse 26/26, total 155/155.

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

lib/go/scoreboard.md

@@ -1,11 +1,11 @@
 # Go-on-SX Scoreboard
 
-**Total: 146 / 146 tests passing**
+**Total: 155 / 155 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | lex | 129 | 129 |
-| ✅ | parse | 17 | 17 |
+| ✅ | parse | 26 | 26 |
 | ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |
 | ⬜ | runtime | 0 | 0 |