go: lex.sx — keywords, ident/int/string/rune lits, comments, ops, ASI + 78 tests [consumes-lex]

First Go-on-SX iteration. Tokenizer consumes lib/guest/lex.sx character-class
predicates. Automatic semicolon insertion per Go spec § Semicolons fires on
newline, EOF, and block comments containing a newline, after
ident/int/string/rune/{break,continue,fallthrough,return}/{++,--,),],}}.

Scoreboard + conformance.sh wired; lex 78/78. Plan Phase 1 sub-items
checked; floats/raw-strings/hex-ints still ⬜.

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

lib/go/scoreboard.md

@@ -0,0 +1,15 @@
+# Go-on-SX Scoreboard
+
+**Total: 78 / 78 tests passing**
+
+|  | Suite | Pass | Total |
+|---|---|---|---|
+| ✅ | lex | 78 | 78 |
+| ⬜ | parse | 0 | 0 |
+| ⬜ | types | 0 | 0 |
+| ⬜ | eval | 0 | 0 |
+| ⬜ | runtime | 0 | 0 |
+| ⬜ | stdlib | 0 | 0 |
+| ⬜ | e2e | 0 | 0 |
+
+Generated by `lib/go/conformance.sh`.