[hooks_runner] Optimize the no hooks path

[dcharkes]

Bug: #2236

Optimize the code paths for when there are no hooks (speeds up standalone Dart).

• Return early in various places, and check if there are hooks at all as first thing.
• Write JSON encoding instead of YAML encoding. 17 ms -> 1 ms on a small JSON object. (And JSON is valid YAML.)

After this the longest running part in dartdev is loading the package_config.json: 10 ms. We can't really avoid this because we need that info to check whether we have any hooks that need running. And the package_config.json isn't already loaded by dartdev (in contrast to flutter_tools where we have a PackageConfig object available). dartdev delegates compilation to package:pub(!) via getExecutableForCommand and that API uses the package config file path. dart-lang/pub#4067

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// 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.

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

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// 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.

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

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// 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

[coveralls]

coverage: 83.667% (-8.0%) from 91.694%
when pulling 1e86a3b on hooks-runner-optimizations
into 5c7152e on main.

[goderbauer]

LGTM

[goderbauer]

I can see a future reader stumbling over this line and wondering why we encode yaml with the Json encoder. Can you leave a comment or fix the naming?