go: parse.sx — unary prefix operators + 11 tests [nothing]

Adds Go unary prefix operators per Go spec § Operators:
  +x  -x  !x  ^x  *p  &v  <-ch

gp-parse-unary is recursive (so !!x and -^x chain correctly) and
sits between gp-parse-expr and gp-parse-primary — unary therefore
always binds tighter than any binary op without needing a unary
entry in the precedence table.

Symbols +, -, *, &, ^ are shared between unary and binary forms;
the positional split (expression-start sees unary, mid-expression
sees binary) disambiguates them cleanly with no lookback.

Unary nodes are single-arg ast-app:
  (ast-app (ast-var OP) (list OPERAND))

parse 37/37, total 166/166.

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: 155 / 155 tests passing**
+**Total: 166 / 166 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | lex | 129 | 129 |
-| ✅ | parse | 26 | 26 |
+| ✅ | parse | 37 | 37 |
 | ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |
 | ⬜ | runtime | 0 | 0 |