feat: add --noclean to prevent cleaning

Picus initially never clean up temporary files. However, the last commit
changed this so that temporary files are cleaned up. Sometimes, though,
we really do not want to clean up files (e.g. in order to generate
smt2 files for debugging purposes). This commit adds the flag to
control whether to run the clean up.

picus.rkt

@@ -18,6 +18,7 @@
 (define arg-r1cs #f)
 (define arg-circom #f)
 (define arg-opt-level #f)
+(define arg-clean? #t)
 (define arg-timeout 5000)
 (define arg-solver "z3")
 (define arg-selector "counter")
@@ -38,6 +39,8 @@
                (when (not (string-suffix? arg-circom ".circom"))
                  (tokamak:exit "file needs to be *.circom"))]
  #:once-each
+ [("--noclean") "do not clean up temporary files (default: false)"
+                (set! arg-clean? #f)]
  [("--opt-level") p-opt-level "optimization level for circom compilation (only applicable for --circom, default: 0)"
                   (set! arg-opt-level
                         (match p-opt-level
@@ -234,4 +237,5 @@
   (when (> arg-cex-verbose 0)
     (format-cex "other bindings" (order other-info))))
 
-(clean-tmpdir!)
+(when arg-clean?
+  (clean-tmpdir!))