Description

This PR adds sharedLock() to Query Builder.

It is the read-lock counterpart to lockForUpdate() and can be used when rows should be protected from concurrent updates while the current transaction reads them:

$db->transaction(static function ($db) use ($accountId): void {
    $account = $db->table('accounts')
        ->where('id', $accountId)
        ->sharedLock()
        ->get()
        ->getRow();
});

Supported drivers:

• MySQLi: LOCK IN SHARE MODE
• Postgre: FOR SHARE
• SQLSRV: table hints

SQLite3 and OCI8 throw a DatabaseException.

The implementation reuses the same internal select-lock path as lockForUpdate(). This keeps reset behavior consistent and ensures helper queries like exists() and countAllResults() do not include select locks while preserving the original builder state.

Docs and tests were added for supported SQL, unsupported drivers, reset behavior, and driver-specific limitations.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide