maude: order-sorted least-sort inference (14 tests, 250 total)

lib/maude/sorts.sx — mau/term-sort computes the least sort of a term (smallest
result sort among op declarations whose arg sorts the actuals satisfy modulo
subsorting); overloaded f(1)=NzNat vs f(s 0)=Nat. mau/has-sort? for
membership-style checks. Answers the plan's order-sorted substrate question.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/maude/conformance.conf

@@ -8,6 +8,7 @@ PRELOADS=(
   lib/guest/pratt.sx
   lib/maude/term.sx
   lib/maude/parser.sx
+  lib/maude/sorts.sx
   lib/maude/reduce.sx
   lib/maude/matching.sx
   lib/maude/conditional.sx
@@ -27,6 +28,7 @@ SUITES=(
   "conditional:lib/maude/tests/conditional.sx:(mau-conditional-tests-run!)"
   "owise:lib/maude/tests/owise.sx:(mau-owise-tests-run!)"
   "gather:lib/maude/tests/gather.sx:(mau-gather-tests-run!)"
+  "sorts:lib/maude/tests/sorts.sx:(mau-sorts-tests-run!)"
   "rewrite:lib/maude/tests/rewrite.sx:(mau-rewrite-tests-run!)"
   "searchpath:lib/maude/tests/searchpath.sx:(mau-searchpath-tests-run!)"
   "strategy:lib/maude/tests/strategy.sx:(mau-strategy-tests-run!)"