go: parse.sx — if/else, for, break/continue, inc-dec + 11 tests [nothing]

Adds the most-used control-flow forms:
  if COND { ... } [else { ... } | else if ...]
  for { ... }                          — infinite
  for COND { ... }                     — while-like
  for INIT; COND; POST { ... }         — C-style
  break / continue                     — keyword stmts (no labels yet)
  x++ / x--                            — Go statement inc-dec

AST shapes:
  (list :if COND THEN ELSE)              — ELSE nil / :if / :block
  (list :for INIT COND POST BODY)        — any of INIT/COND/POST may be nil
  (list :break LABEL)  (list :continue LABEL)
  (list :inc-dec OP EXPR)                — OP is "++" / "--"

**Closes the parser-mode caveat** logged when composite literals
landed. `gp-no-comp-lit` is a re-entrant counter on the parser state;
control-flow constructs increment it before parsing their condition
and decrement after, suppressing the postfix `{` → composite-lit
interpretation so that `if Foo { ... }` correctly reads `{ ... }` as
the body, not as `Foo{}` composite literal. Verified by the test:

  (go-parse "if Foo {}")  →  (:if (:var "Foo") (:block ()) nil)

gp-parse-control-cond is the single helper that bracket-wraps the
flag bump so future control-flow forms (switch, select, range) can't
forget to engage suppression.

switch / select / defer / go / for-range / channel-send still deferred.

parse 152/152, total 281/281.

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

lib/go/scoreboard.json

@@ -1,10 +1,10 @@
 {
   "language": "go",
-  "total_pass": 270,
-  "total": 270,
+  "total_pass": 281,
+  "total": 281,
   "suites": [
     {"name":"lex","pass":129,"total":129,"status":"ok"},
-    {"name":"parse","pass":141,"total":141,"status":"ok"},
+    {"name":"parse","pass":152,"total":152,"status":"ok"},
     {"name":"types","pass":0,"total":0,"status":"pending"},
     {"name":"eval","pass":0,"total":0,"status":"pending"},
     {"name":"runtime","pass":0,"total":0,"status":"pending"},