New Apple IPencil and charging

Your Apple Pencil will come to no harm whatsoever in being docked with your iPad for extended periods.

It is generally recommended that your Apple Pencil Pro should be kept docked with the host iPad when not in active use - as this ensures that the tiny internal battery is kept optimally charged when idle.  Charging only occurs when the battery requires charge from the iPad, optimal charge being entirely automatic.

Keeping the Pencil separated from the iPad when unused risks allowing its battery to discharge; if allowed to remain in this state, the battery may fall into a state of deep discharge, this being a state from which it may never recover. When the Pencil battery fails, the only remedy is to replace the entire Pencil; the battery itself is not a serviceable item.

Charge your Apple Pencil and check the battery - Apple Support

In more detail, all rechargeable batteries, regardless of battery chemistry, require maintenance through periodic charging. In this regard, the battery within the Apple Pencil is no different to any other device that is powered by an internal Li-ion battery.

If your Pencil is set-aside for an extended period, unused and uncharged, the Pencil battery may have be irretrievably damaged through deep discharge. In common with all Li-ion batteries, they must always have some level of charge. The tiny internal Li-ion battery is susceptible to permanent/irreversible damage through being left discharged for long periods. Even some “new” pencils can exhibit signs of failure out-of-the-box if they are “old stock”. 

It is essential that if you have an Apple Pencil that you charge it regularly - whether used or not - so as to protect the battery from deep-discharge. Never allow a pencil to remain in low-charge state for any period of time - as the internal battery may fail, rendering the Pencil useless. Setting aside an unused Pencil, for extended periods, is a recipe for premature death of the Pencil battery.

Yes — you can safely leave the new Apple Pencil Pro attached to your iPad Pro (M4) all the time, and in fact, Apple designed it to be stored and charged that way.