test: Update fuzzer tests to use new create_finding signature

Fixed failing unit tests that were using the old create_finding() signature.
The native findings format refactoring added two new required parameters:
- rule_id: Identifier for the rule/pattern that detected the finding
- found_by: FoundBy object with module, tool, and detection type info

Updated tests:
- test_cargo_fuzzer.py::test_create_finding_from_crash
- test_atheris_fuzzer.py::test_create_crash_finding

Both tests now properly instantiate FoundBy objects with appropriate
fuzzer metadata (module name, tool name, version, and type="fuzzer").

backend/tests/unit/test_modules/test_atheris_fuzzer.py

@@ -159,11 +159,20 @@ class TestAtherisFuzzerFindingGeneration:
 
     async def test_create_crash_finding(self, atheris_fuzzer):
         """Test crash finding creation"""
+        from models.finding_schema import FoundBy
+
         finding = atheris_fuzzer.create_finding(
+            rule_id="atheris-crash",
             title="Crash: Exception in TestOneInput",
             description="IndexError: list index out of range",
             severity="high",
             category="crash",
+            found_by=FoundBy(
+                module="atheris_fuzzer",
+                tool_name="Atheris",
+                tool_version="2.3.0",
+                type="fuzzer"
+            ),
             file_path="fuzz_target.py",
             metadata={
                 "crash_type": "IndexError",

backend/tests/unit/test_modules/test_cargo_fuzzer.py

@@ -161,11 +161,20 @@ class TestCargoFuzzerFindingGeneration:
 
     async def test_create_finding_from_crash(self, cargo_fuzzer):
         """Test finding creation"""
+        from models.finding_schema import FoundBy
+
         finding = cargo_fuzzer.create_finding(
+            rule_id="cargo-fuzz-crash",
             title="Crash: Segmentation Fault",
             description="Test crash",
             severity="critical",
             category="crash",
+            found_by=FoundBy(
+                module="cargo_fuzz",
+                tool_name="cargo-fuzz",
+                tool_version="0.11.2",
+                type="fuzzer"
+            ),
             file_path="fuzz/fuzz_targets/fuzz_target_1.rs",
             metadata={"crash_type": "SIGSEGV"}
         )