maude: mixfix surface-syntax printer (11 tests, 207 total)

lib/maude/pretty.sx — mau/term->maude renders internal prefix terms back
in Maude mixfix syntax driven by op forms; mau/red->maude / mau/rew->maude
reduce-then-render. Output now reads as idiomatic Maude.

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

lib/maude/conformance.conf

@@ -15,6 +15,7 @@ PRELOADS=(
   lib/maude/rewrite.sx
   lib/maude/strategy.sx
   lib/maude/meta.sx
+  lib/maude/pretty.sx
 )
 
 SUITES=(
@@ -25,4 +26,5 @@ SUITES=(
   "rewrite:lib/maude/tests/rewrite.sx:(mau-rewrite-tests-run!)"
   "strategy:lib/maude/tests/strategy.sx:(mau-strategy-tests-run!)"
   "meta:lib/maude/tests/meta.sx:(mau-meta-tests-run!)"
+  "pretty:lib/maude/tests/pretty.sx:(mau-pretty-tests-run!)"
 )