Crash with custom Decodable property that is not a command line option

[Jomy10]

When a property in a ParsableCommand has a custom Decodable implementation, but it is not a Flag, Option or Argument, and the custom decodable implementation uses nestedContainer, the program will crash.

The crash is the following:

ArgumentParser/ArgumentDecoder.swift:135: Fatal error
[1]    77018 illegal hardware instruction  [executable path] --help

ArgumentParser version: 1.5.0
Swift version: Paste the output of swift --version here.

swift-driver version: 1.62.15 Apple Swift version 5.7.2 (swiftlang-5.7.2.135.5 clang-1400.0.29.51)
Target: x86_64-apple-macosx13.0

Checklist

• If possible, I've reproduced the issue using the main branch of this package
• I've searched for existing GitHub issues

Steps to Reproduce

@main
struct Main: ParsableCommand {
  var property: MyCustomDecodableStruct = MyCustomDecodableStruct()
}

struct MyCustomDecodableStruct: Decodable {
  enum CodingKeys: String, CodingKey {
    case input
    case output
  }
  enum InputCodingKeys: String, CodingKey {
    case inputLanguage = "language"
  }

  enum OutputCodingKeys: String, CodingKey {
    case outputLanguage = "language"
  }

  init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    let input = try container.nestedContainer(keyedBy: InputCodingKeys.self, forKey: .input)
    let output = try container.nestedContainer(keyedBy: OutputCodingKeys.self, forKey: .output)

    /* rest of the implementation */
  }
}

Expected behavior

This property should be ignored

Actual behavior

ArgumentParser/ArgumentDecoder.swift:135: Fatal error
[1]    77018 illegal hardware instruction  [executable path] --help

Sidenote

Important to note is that on Swift 5.7, this will cause the compiler to crash in debug mode, but not in release mode