go: lex.sx — raw string literals (backtick) + 9 tests [nothing]

Adds Go raw string literals per Go spec § String literals:
backtick-delimited, no escape processing, may span multiple
lines, '\r' chars discarded from the value.

gl-read-raw-string! mirrors gl-read-string! but skips escape
handling and the \r filter. scan! routes the leading backtick
to it; emits "string" type (same as interpreted strings — no
need to distinguish at parse/type time).

lex 123/123.

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

lib/go/scoreboard.json

@@ -1,9 +1,9 @@
 {
   "language": "go",
-  "total_pass": 114,
-  "total": 114,
+  "total_pass": 123,
+  "total": 123,
   "suites": [
-    {"name":"lex","pass":114,"total":114,"status":"ok"},
+    {"name":"lex","pass":123,"total":123,"status":"ok"},
     {"name":"parse","pass":0,"total":0,"status":"pending"},
     {"name":"types","pass":0,"total":0,"status":"pending"},
     {"name":"eval","pass":0,"total":0,"status":"pending"},