[salilg-eng]

Fixes #1182

Description:
When using is_readable or stat via the PHP stream wrapper, the library currently tries to determine the stat mode by calling $this->bucket->isWritable(). This triggers an expensive Class-A API call (getResumeUri) to write an empty object. This leads to high latency, additional cost, and failure on read-only buckets.
This PR introduces an opt-in bypass feature using stream context options. By setting stat_permission_check => false in the stream context for the gs protocol, users can safely bypass this API call. When bypassed, the stream wrapper will optimistically assume the bucket has read/write permissions (mode 100666), deferring actual permission checks to the subsequent read/write operations (which correctly throw 403 if unauthorized).
Example Usage:

stream_context_set_default([
    'gs' => ['stat_permission_check' => false]
]);
is_readable('gs://my-bucket/file.txt'); // No Class-A network call is made

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[kalragauri]

Please use standard GitHub closing syntax in the PR description so the public issue is linked properly: Fixes #1182