enhance(tests): Add option use_default_fhe_constraints to YAML test descriptions

This adds a new optional boolean parameter
`use_default_fhe_constraints` to the YAML description of tests that
causes the test backend to use the default FHE constraints if set to
true. This is necessary for clear text tests, since automatic
determination of FHE parameters by the `CompilerEngine` fails for
programs not using encrypted integers and causes the program to abort.

compiler/tests/end_to_end_fixture/EndToEndFixture.cpp

@@ -8,6 +8,8 @@
 
 using mlir::concretelang::StreamStringError;
 
+const mlir::concretelang::V0FHEConstraint defaultV0Constraints{1, 1};
+
 // derived from https://stackoverflow.com/a/45869209
 uint64_t solve_binomial_cdf_bigger_than(size_t n, double p_error,
                                         double p_mass) {
@@ -247,6 +249,13 @@ template <> struct llvm::yaml::MappingTraits<EndToEndDesc> {
     io.mapRequired("description", desc.description);
     io.mapRequired("program", desc.program);
     io.mapRequired("tests", desc.tests);
+
+    bool use_default_fhe_constraints = false;
+    io.mapOptional("use_default_fhe_constraints", use_default_fhe_constraints);
+
+    if (use_default_fhe_constraints)
+      desc.v0Constraint = defaultV0Constraints;
+
     std::vector<int64_t> v0parameter;
     io.mapOptional("v0-parameter", v0parameter);
     if (!v0parameter.empty()) {