Add --max-stack / -s flag to limit stack depth (#637)

## Summary
- Adds a `--max-stack` / `-s` CLI flag (default 500) to limit the
evaluation stack depth, matching go-jsonnet's `-s` / `--max-stack`
option.
- Introduces a stack frame counter in the Evaluator,
incremented/decremented at function calls (`Apply*`, `ApplyBuiltin*`),
object field evaluation (`invoke`), imports, and default parameter
evaluation.
- When the counter exceeds `maxStack`, a clear `sjsonnet.Error: Max
stack frames exceeded.` is thrown instead of a raw JVM
`StackOverflowError`.

## Test plan
- [x] JVM tests pass (140/140)
- [x] WASM tests pass (333/333)
- [x] New unit tests for recursive functions, mutual recursion, depth
within limits, and builtin calls
- [x] Golden files updated for `error.recursive_function_nonterm`,
`error.recursive_import`, `error.recursive_object_non_term`, and
`error.function_infinite_default`
- [x] CLI flag verified with `--max-stack` and `-s` short form

Author: stephenamar-db

build.mill

@@ -78,8 +78,8 @@ trait SjsonnetCrossModule extends CrossScalaModule with ScalafmtModule {
         "-feature",
         "-opt-inline-from:sjsonnet.*,sjsonnet.**",
         "-Xsource:3",
-        "-Xlint:_"
-      ) ++ (if (scalaVersion().startsWith("2.13")) Seq("-Wconf:origin=scala.collection.compat.*:s")
+        "-Xlint:_",
+      ) ++ (if (scalaVersion().startsWith("2.13")) Seq("-Wopt", "-Wconf:origin=scala.collection.compat.*:s")
             else Seq("-Xfatal-warnings", "-Ywarn-unused:-nowarn"))
     else Seq[String]("-Wconf:origin=scala.collection.compat.*:s", "-Xlint:all")
   )

sjsonnet/src-jvm-native/sjsonnet/Config.scala

@@ -161,6 +161,12 @@ final case class Config(
       doc = "Print runtime statistics (thunks, calls, imports, timing) to stderr after evaluation"
     )
     debugStats: Flag = Flag(),
+    @arg(
+      name = "max-stack",
+      short = 's',
+      doc = "Number of allowed stack frames (default 500)"
+    )
+    maxStack: Int = 500,
     @arg(
       doc = "The jsonnet file you wish to evaluate",
       positional = true

sjsonnet/src-jvm-native/sjsonnet/SjsonnetMainBase.scala

@@ -155,7 +155,8 @@ object SjsonnetMainBase {
           strict = config.strict.value,
           throwErrorForInvalidSets = config.throwErrorForInvalidSets.value,
           maxParserRecursionDepth = config.maxParserRecursionDepth,
-          brokenAssertionLogic = config.brokenAssertionLogic.value
+          brokenAssertionLogic = config.brokenAssertionLogic.value,
+          maxStack = config.maxStack
         ),
         parseCache,
         wd,