Add Oracle database connection configuration and robustness improvements

[Copilot]

The repository lacked database driver support and configuration parameters for Oracle DB.

This pull request introduces Oracle connection capabilities to the database service registry, ensuring compatibility with Oracle databases and isolated environment configurations.

Database Configuration

• Added the oracle database connection block to config/database.php utilizing unique ORACLE_DB_ environment variables to prevent host/credential namespace collisions with primary databases.

'oracle' => [
    'driver' => 'oracle',
    'host' => env('ORACLE_DB_HOST', '127.0.0.1'),
    'port' => env('ORACLE_DB_PORT', '1521'),
    'database' => env('ORACLE_DB_DATABASE', 'xe'),
    'username' => env('ORACLE_DB_USERNAME', 'system'),
    'password' => env('ORACLE_DB_PASSWORD', ''),
    'charset' => env('ORACLE_DB_CHARSET', 'AL32UTF8'),
    'prefix' => env('ORACLE_DB_PREFIX', ''),
    'prefix_indexes' => true,
],

Environment Templates

• Updated .env.example with standard Oracle configuration keys and documented default fallback values.

Test Coverage & Robustness

• Added tests/Unit/OracleDatabaseConfigTest.php to verify full resolution, driver mapping, default fallback integrity, and prefix options.
• Patched floating-point precision comparisons in tests/Unit/InventoryTotalCostTest.php using rounding to eliminate flaky test runs.