feat: saveMany() now injects timestamps

[techmahedy]

Problem

saveMany() was calling insertMany() directly without adding timestamps,
even when $timeStamps = true on the model, though it was intentional previously. But now it supports $timeStamps = true

Before Fix

name	email	created_at	updated_at
John Doe	john@test.com	NULL	NULL
Jane Doe	jane@test.com	NULL	NULL

After Fix

name	email	created_at	updated_at
John Doe	john@test.com	2026-03-11 08:30:00	2026-03-11 08:30:00
Jane Doe	jane@test.com	2026-03-11 08:30:00	2026-03-11 08:30:00

Changes

• saveMany() now checks $timeStamps on the model before bulk insert
• created_at is only set if not already provided by the caller
• updated_at is always set to current time
• Respects #[CastToDate] attribute for date-only timestamps, consistent with save() and create()