Type predicates, arithmetic, chars (inline α/digit/case),
format, gensym, values, sets, radix, list utilities.
cl-empty? guards all list traversal against () vs nil in sx_server.
Load spec/stdlib.sx in test.sh to expose format.
Fix lib/r7rs.sx number->string to use (= (len r) 0) not (nil? r).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
