fix: std.parseJson reports truncated input cleanly

Motivation: Truncated std.parseJson input could surface incomplete parser failures poorly.

Modification: Map incomplete ujson parse failures to clean sjsonnet errors and add regressions.

Result: Truncated JSON input now reports a clear user-facing parse error.

Author: He-Pin

sjsonnet/src/sjsonnet/stdlib/ManifestModule.scala

@@ -130,6 +130,8 @@ object ManifestModule extends AbstractFunctionModule {
       } catch {
         case e: ujson.ParseException =>
           throw Error.fail("Invalid JSON: " + e.getMessage, pos)(ev)
+        case _: ujson.IncompleteParseException =>
+          throw Error.fail("Invalid JSON: unexpected end of JSON input", pos)(ev)
       }
     }
   }

sjsonnet/test/resources/new_test_suite/error.parsejson_empty_input.jsonnet

@@ -0,0 +1 @@
+std.parseJson("")

sjsonnet/test/resources/new_test_suite/error.parsejson_empty_input.jsonnet.golden

@@ -0,0 +1 @@
+sjsonnet.Error: [std.parseJson] Invalid JSON: unexpected end of JSON input

sjsonnet/test/resources/new_test_suite/error.parsejson_truncated_input.jsonnet

@@ -0,0 +1 @@
+std.parseJson('{"a":')

sjsonnet/test/resources/new_test_suite/error.parsejson_truncated_input.jsonnet.golden

@@ -0,0 +1 @@
+sjsonnet.Error: [std.parseJson] Invalid JSON: unexpected end of JSON input