feat(storage): add deleteSourceObjects option to Bucket::compose()

[salilg-eng]

Overview

This Pull Request implements support for the native GCS server-side auto-deletion of source objects when merging files using Bucket::compose().

When the option deleteSourceObjects => true is supplied, GCS natively handles the sequential cleanup of intermediate component files on the server-side, making the composition operation immeasurably faster, safer, and completely transaction-secure.

Architecture & Design Decisions

• Native Request Body Serialization:
  Instead of sending deleteSourceObjects as a URL query parameter or running a manual client-side cleanup loop, this implementation fully integrates the option inside the JSON request body payload (ComposeRequest properties).
• Zero Client-side Overhead:
  Completely delegates the deletion process to the GCS backend. The library makes exactly one single POST call to objects.compose without spawning any local deletion loops, catching errors, or making redundant connection calls.
• API Spec Alignment:
  Updated the API service discovery spec (storage-v1.json) to define deleteSourceObjects inside the ComposeRequest body properties, while removing it from the URL query parameters. This allows Guzzle's RequestBuilder to naturally handle request mapping and serialization.

Changes

1. Storage/src/Bucket.php:
   • Declared deleteSourceObjects inside the compose() method docstrings.
   • Erased all legacy client-side deletion loops, validation unsets, and error handlers to fully leverage GCS server-side native capability.
2. Storage/src/Connection/ServiceDefinition/storage-v1.json:
   • Removed deleteSourceObjects from the query parameter metadata list of the objects.compose method.
   • Added deleteSourceObjects as a boolean property under the ComposeRequest request body schema.
3. Storage/tests/Unit/BucketTest.php:
   • Added mock test case verifying Guzzle serializes deleteSourceObjects => true inside the request body parameters.
   • Confirms that no local connection calls to deleteObject() are spawned.
4. Storage/tests/System/ManageObjectsTest.php:
   • Includes live GCS E2E integration test cases matching standard GCS behavior options (true, false, null).

Verification & Testing

All unit tests have been successfully verified and pass with a 100% success rate locally:

• Result: OK (64 tests, 111 assertions)

[salilg-eng]

Hi maintainers,

The single PHPStan Static Analysis failure is a preexisting upstream repository issue and is completely unrelated to the changes in this PR.

This PR strictly modifies 4 files under the Storage package, which is 100% static-analysis green. The failure occurs entirely under the Spanner component due to the release of PHPStan 2.2.0 yesterday (May 28).

Since the CI workflow uses composer update -d dev on every run, the build automatically pulled the new 2.2.0 release which has stricter sealed array validation rules, flagging preexisting array shapes inside Spanner/src/ValueMapper.php and Spanner/src/Operation.php. Upstream main commits analyzed before yesterday passed solely because they ran under the older 2.1.56 release.

Ready for a final look and merge!

[kalragauri]

Please update the PR description to match the updated implementation.

[kalragauri]

nit: remove extra blank line.

[salilg-eng]

Removed space