fix(lang): a template inside another's hole, and integer literals past 2^31 - 1

A template literal nested in a {...} hole crashed the parser: the outer
literal ended at the inner backtick. The lexer (and ludic-fmt's) now
reads a hole as code, taking strings, chars and templates in it whole.
A decimal literal past 2147483647, or a hex one of more than eight
digits, was wrapped into a negative int; it is a long with its value
now, and giving one to an int is refused. Reseed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/rejected/long_into_int.ludic

@@ -0,0 +1,7 @@
+# a literal past 2^31 - 1 is a long, and a long does not narrow into an int
+program LongIntoInt {
+  entry {
+    let n: int = 4294967295
+    print(n)
+  }
+}