GUEST: step 3 — lib/guest/lex.sx character-class + token primitives

Extracted shared tokeniser primitives:
- Char-class predicates: lex-digit?, lex-hex-digit?, lex-alpha?
  (alias lex-letter?), lex-alnum?, lex-ident-start?, lex-ident-char?,
  lex-space? (no newline), lex-whitespace? (incl newline). All nil-safe.
- Token record: lex-make-token, lex-make-token-spanning, accessors.

Ported lib/lua/tokenizer.sx and lib/tcl/tokenizer.sx — 7 lua and 5 tcl
predicate definitions collapsed into prefix-rename calls that alias
lua-/tcl- names to lex- primitives. Test scripts (lua/test.sh,
tcl/test.sh, tcl/conformance.sh) load lib/guest/lex.sx and prefix.sx
before the per-language tokenizer.

Verification:
- lua/test.sh: 185/185 = baseline
- tcl/test.sh: 342/342 (parse 67 + eval 169 + error 39 + namespace 22
                       + coro 20 + idiom 25)
- tcl/conformance.sh: 3/4 = baseline (event-loop failure is pre-existing)

Two consumers verified — step complete.

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

lib/lua/test.sh

@@ -28,6 +28,8 @@ trap "rm -f $TMPFILE" EXIT
 
 cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1)
+(load "lib/guest/lex.sx")
+(load "lib/guest/prefix.sx")
 (load "lib/lua/tokenizer.sx")
 (epoch 2)
 (load "lib/lua/parser.sx")