[jnigen] Support use arenas on nullable JObjects

[dickermoshe]

The use method makes it really easy to use jni and not worry about memory management (even if the nesting get's ugly)

However this PR allows you to use use on nullable JObject?s too.
This is a very small pr which would allow you to do this.

someFunc(JObject? obj){
  obj.use(...);
}

The extension was only on JObject previosly.

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[HosseinYousefi]

The use method has existed for a while however I don't really recommend using it anymore (due to excessive nesting as you mentioned). We might even be fine with removing it eventually for 1.0. Instead use using:

using((arena) {
  final foo = Foo()..releasedBy(arena);
  final bar = Bar(foo)..releasedBy(arena);
});
// Now both foo and bar are released and we didn't have to nest twice.

I'm fine with landing your change though for now once you fix the test and add a changelog entry.

[dickermoshe]

What should the wip header of the changelog be?

[HosseinYousefi]

What should the wip header of the changelog be?

Actually, it's not a big change. So let's ignore the changelog.

[github-actions]

PR Health

Breaking changes ⚠️

Package	Change	Current Version	New Version	Needed Version	Looking good?
jni	Breaking	0.14.1	0.14.1	0.15.0 Got "0.14.1" expected >= "0.15.0" (breaking changes)	⚠️

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Changelog Entry ❗

Package	Changed Files
package:jni	pkgs/jni/lib/src/jobject.dart

Changes to files need to be accounted for in their respective changelogs.

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API leaks ⚠️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbols
jni	_ReferenceType _opaque_pthread_mutex_t _opaque_pthread_cond_t _Dart_FinalizableHandle

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License Headers ✔️

// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

Files
no missing headers

All source files should start with a license header.

Unrelated files missing license headers

Files
pkgs/jni/lib/src/third_party/generated_bindings.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

[HosseinYousefi]

Please run dart format on the test to satisfy the CI!

[dickermoshe]

Done

[HosseinYousefi]

analyze_jni step fails:

   info • Use 'const' for final variables initialized to a constant value • test/jobject_test.dart:178:5 • prefer_const_declarations

[dickermoshe]

@HosseinYousefi Sorry that this became this many tries on my part.
Passes analyze and format. now.

[coveralls]

coverage: 79.391% (+1.0%) from 78.421%
when pulling 3c47546 on dickermoshe:patch-2
into dcc6fc9 on dart-lang:main.

[HosseinYousefi]

LGTM! Thanks!