[main] [bug] Catch RequestException instead of Throwable in DatabaseDelete

[JoshSalway]

Fixes #46

Summary

DatabaseDelete catches Throwable instead of RequestException. This catches everything including TypeError, OutOfMemoryError, and other non-API errors, masking real bugs as "Failed to delete database" messages. All other delete commands catch RequestException.

Proof

BEFORE: catch(Throwable) - current code
  API error (RequestException): CAUGHT - shown as 'Failed to delete database'
  Type bug (TypeError): CAUGHT - shown as 'Failed to delete database'
  Memory crash (Error): CAUGHT - shown as 'Failed to delete database'
  Bad method call: CAUGHT - shown as 'Failed to delete database'

AFTER: catch(RequestException) - this PR
  API error (RequestException): CAUGHT - friendly API error message
  Type bug (TypeError): NOT CAUGHT - propagates correctly as TypeError
  Memory crash (Error): NOT CAUGHT - propagates correctly as Error
  Bad method call: NOT CAUGHT - propagates correctly as BadMethodCallException

Before / After

// Before - catches everything, masks real bugs:
use Throwable;

} catch (Throwable $e) {
    error('Failed to delete database: '.$e->getMessage());
}

// After - only catches API errors, consistent with other delete commands:
use Saloon\Exceptions\Request\RequestException;

} catch (RequestException $e) {
    error('Failed to delete database: '.$e->getMessage());
}

Consistency

Every other delete command already catches RequestException:

• ApplicationDelete
• BackgroundProcessDelete
• DatabaseClusterDelete
• DomainDelete
• EnvironmentDelete
• InstanceDelete

DatabaseDelete was the only outlier.