[12.x] Add *OrFail transaction methods to BelongsToMany

[SanderMuller]

Adds syncOrFail(), syncWithoutDetachingOrFail(), attachOrFail(), detachOrFail(), and toggleOrFail() to the BelongsToMany relationship, wrapping each operation in a database transaction.

This follows the existing saveOrFail() / deleteOrFail() / updateOrFail() convention on Model. While single-query operations like attach(1) are already atomic, multi-query operations like sync() and toggle() perform detaches and attaches in sequence. If one fails partway through, the pivot table is left in a partial state. These methods guarantee all-or-nothing behavior.

New methods

Method	Wraps
syncOrFail($ids, $detaching)	sync()
syncWithoutDetachingOrFail($ids)	syncWithoutDetaching()
attachOrFail($id, $attributes, $touch)	attach()
detachOrFail($ids, $touch)	detach()
toggleOrFail($ids, $touch)	toggle()

Each method is placed directly after its base counterpart in the InteractsWithPivotTable trait.

Usage

  // Sync roles atomically — rolls back if any query fails
  $user->roles()->syncOrFail([1, 2, 3]);

  // Attach within a transaction (useful with custom pivot classes)
  $user->roles()->attachOrFail($roleId, ['expires_at' => now()->addYear()]);

Test plan

• testSyncOrFail — verifies sync returns correct attached/detached/updated arrays
• testSyncWithoutDetachingOrFail — verifies existing attachments are preserved
• testAttachOrFail — verifies basic attach
• testAttachOrFailWithAttributes — verifies pivot attributes are set
• testDetachOrFail — verifies partial detach returns correct count
• testDetachOrFailAll — verifies detach with no args removes all
• testToggleOrFail — verifies toggle attaches/detaches correctly